Anyone using it?
Just playing with it now - not as polished as inDesign but it has some interesting qualities
Any drawbacks of using it as a primary design environment for type?
No OpenType features support of any kind, neither simple nor complex scripts. The development branch have some preliminary work to support OpenType but it may be a year or two before being releasable (if ever, they have been promising OpenType support for years now).
I'm using it as a prior design environment.
Some drawbacks : no OpenType advanced features, tedious text handling (some improvements on the way for the next version for the latter problem ; same goes for color — ginger koons is working on it: http://www.adaptstudio.ca/blog/2010/06/a-talk-about-open-colour.html)
Pros: of course the price, multi-plateform, and open editing format
The drawbacks are obviously overwhelmed by the pros, as you'll see in practice ;-)