As a Lion user, I have to say I'm not a fan of switching to the OS's fullscreen mode, primarily because I work with two monitors, and it's pretty much useless in that configuration.
The old fullscreen mode was much better for a few reasons:
- you could cmd-` between two projects in fullscreen mode
- you could have ST2 in fullscreen on monitor 1 and your File Manager/FTP app in monitor 2 (or Netflix streaming .. or Terminal)
- the transition between fullscreen and non-fullscreen wasn't a full second of sliding, oozing, fading fullscreen animation (I'm on a 13" c2d mbp, not so speedy)
- more I'm sure, this was just in the first 5 seconds of trying to use it...
I've never been a fan of Spaces on OS X, and shoehorning apps-as-fullscreen in as a Space seems to be fine for work on your MacBook, but we dinosaur powernerds on 24"+ dual screen setups are left out of the equation.
Maybe this is behavior we'll see fixed in 10.7.1, but I doubt it. And I'm sure maintaining two types of fullscreen mode in ST2 would be as much of a pain as it would be confusing for users.