• Command-Tab Foregrounding: when I switch to an app, I expect it to be foregrounded.  For non-full screen apps, I am more often moved to the space it’s in, but left looking at the most recently foregrounded app in that space.
• Command-Tab Recent Apps: I have 2 full-screen Safari windows open.  I am looking at one of these, and Command-Tab over to Terminal.  I now Command-Tab back.  I get the other Safari window presented, but if I look hard, it has the backgrounded look (grayscale buttons, low contrast, etc.).  If I hit Command-L, to jump to the URL bar, in this state, Lion will now switch me to the other Safari window.  It knows it’s wrong!  Hitting Command-T to open a new tab also seems to have the effect of opening a tab in the non-visible Safari window in this state, though it doesn’t cause a switch to the other window.
• Intra-App Window Switching: more generally, if there are multiple full-screen windows for a given app, only the “foreground” window of that app (which I seem to have no control over, as noted above) is available through Command-Tab switching.  Combine that with the fact that Command-Backtick no longer works between full-screen windows in an app, and I now must use gestures to access certain windows.  Productivity killer for a programmer. 
• Desktop Inaccessible: None of the Expose gestures that get me to the desktop work while I’m in a full-screen app.  Picky, maybe, but I had a big use case here, which was that I’d grab an image out of a web page in Safari, flick a gesture to expose the desktop, and deposit it there.  The default four-finger gesture to expose the desktop also doesn’t work when you’re dragging anything (it seems to interpret your other fingers’ movement as a 3-fingered swipe, ignoring the finger that’s “holding” the item you’re dragging).  I think the desktop metaphor is awesome, but if I can’t easily drag content from an app onto my desktop, I’ve effectively lost it.

It feels like Lion is a half-way point to a full-screen OS a la iOS, but it is horribly painful to use in the mean time.  There’s a loss in reliability and transparency, and much of what I’m seeing has to qualify as pure bugginess.

I could write a list of the things I think are amazing, well designed, and pretty (the gestures are so great, and OMG the animation for sliding back in Safari history is a work of art), but right now all I want to do is vent. :)

Lion feels like OSY 1.0.  A kind of a new thing, not entirely thought-through, and in desperate need of some polish.