Can URL’s contain spaces (or %20)? Be careful about removing and/or adding “www”, as some sites will not work without it and some sites will not work with it (ex: myblog.blogspot.com).

All lowercase is ok.

Not?

Regarding typesetting: IIRC at least in the German-speaking part of the world we have a convention that when a URL starts with «www.», it's OK to omit the standard «http://» protocol (because it will be sufficiently clear that [1] yes this is a URL and [2] that's where it starts, it can be entered into a browser like this); but if it starts with anything else, you should include the «http://» to make it clearer.

So:

Bringhurst, Robert. The Elements of Typographic Style. Vancouver: Hartley and Marks, 1992, 1997. www.typographicstyle.com

Bringhurst, Robert. The Elements of Typographic Style. Vancouver: Hartley and Marks, 1992, 1997. http://subdomain.typographicstyle.com

I agree with Jens though that if there are URLs nearby using any other protocols, it's probably best to always cite the «http://» so as to avoid ambiguity.

It may boil down to what exactly you mean by "is it okay?" From a functional standpoint, it's probably okay as long as none of the URLs begin with "https" or "ftp". But from a style standpoint, I think you'll find that the style guides say to spell it out in citations, to avoid any ambiguity.

The American Psychological Association publication guidelines say:

Author, A. A. (1997). Title of work. Location, Publisher. Retrieved from http://www.xxxxxx

Depending on what you are referencing (book, journal, presentation &c) the first portion will change, but for the most part, if there is a url, it ends with "Retrieved from..." case sensitive, include http://, and don't end it with a period.

And I agree with James. When in doubt, ask the editor/publiser/boss if they have a convention in place.

Domain names (including top level domains) are not case sensitive.

Everything else in URLs on Unix/Linux machines is generally case sensitive.

If academic writing you have to follow the appropriate standard (APA, MLA, etc).

This is a good guide to APA
http://owl.english.purdue.edu/owl/resource/560/01/

In terms of type, I sometimes use loose tracking for URLs.

John — I’ve also taken to setting URLs in italic, when feasible, to separate them from surrounding text. As you say, it’s a practical aid.

@ John and Kent: In academic publications specifically, would not italicizing urls interfere with visual search when scanning the references due to the fact that book titles or journal names use the same typographic cue?

Personally, I would consider italic urls to be a typographic heirarchy that is incongruent with the informational hierarchy resulting in increased time and decreased accuracy when searching for specific information in a references section.

This would actually make an interesting (and easily testable) experiment.

@neverblinke: While it may create an uneven rag, the only logical conclusion to avoid the hyphen to be misinterpreted as part of the url would be to set it on it's own line. Even then, it may be to long. In an electronic context, auto-detection should take care of it, in print I guess readers would have to go trial and error. An interesting point for consideration. Alternatives may include condensed typefaces, smaller point size or reduced inter-letter spacing.

And what about just forgetting the hyphen and continue the URL on the next line?

IIRC, that’s what the German computer magazine c’t does.

Cristobal: And what about just forgetting the hyphen and continue the URL on the next line?
That’s the default behaviour of InDesign.

Frode: Many designers think underlines are bad in print, but I happen to think nothing signals a hyperlink better.
I tried, but my descenders weren’t happy! ;-) (I’m talking black & white)

I often need to place URIs in notes and bibliographies (http://www.typophile.com/node/74680) and I have even considered to put up an URL shortening service just for it!
Two notes: it would be nice if http://www.example.com/ could be shortened to example.com, but too many websites haven’t even configured the www-less domain.
About italics, it’s tempting, but, as Christopher rightly points out, it didn’t work in references. My first instinct would be setting them in a monospaced font, but they would end up even longer! Maybe, with the right superfamily, they could be set in a light sans if the remaining text is set in a serif face.

I don't think URLs should be hyphenated, as the reader might think the hyphen is part of the URL.

It's often possible to keep a URL on line line if you tinker with the paragraph's line breaks or tighten the tracking a tad. But if breaking it is the only option, I break without a hyphen.

Incidentally, in InDesign I always apply the "no break" attribute to URLs. There are several ways to apply this attribute, but the method I use is to create a character style called "URL", set the style's attributes to include "no break", and then I apply that style to every URL.

re: breaking across line ends - the instructions I've given our typesetters, for URLs in references, are:

1. Don't introduce hyphens;
2. Try not to break at a hyphen that is actually part of the address, lest it look like you've introduced it;
3. Break after a slash, underscore, question mark, or escaped character code (such as "%20"), or before a period (carrying the period over to the next line is sufficiently different-looking from normal sentence punctuation to make it perfectly clear the period is not signalling the end of the sentence/reference)
4. If necessary, where a URL consists of words mashed together (thisisanexample.com) then break between those words.

In body text, the extra spacing is good - even letterspacing and/or a monospaced font or different font.

The logic of italics is good but the flavor does not seem right to me - too informal.

Absolutely no underlining - that not only looks bad but obscures any underscores in the URL. Absolutely no introduced hyphens.

Brackets is a nice idea and I've seen it done well.

You can’t put a space in a the domain name you are discussing. %20 is an encoded space and is an error. Remove it and don’t look back.

Those same domain names are case-insensitive; hostnames like blog. or m. or even www. are not necessarily case insensitive but almost always are. You do not have to act as though [single word].[top-level-domain] is ever case-sensitive despite what you are being told here.

You may nonetheless wish to use the capitalization in your example to improve readability.

In print you have no reason to include the protocol identifier http://, but if the text you are using will at any time be exported to an E-book, you trigger the problem of producing an URL that isn’t usable online because you took the protocol identifier out. You can fix this manually, as I have done, but it’s an extra step.

Eliason, less-than and greater-than are not “brackets”; there is no reason to delimit an URL in plain text unless some statistically improbable character immediately follows it, like maybe a plain hyphen-minus.

Monospaced font (not Courier) can be nice for URLs in print.

You could just do what I have done and call it a day, since my way is correct. I can send you examples.