Half assed effort:
-No character count in SMS window
-No ability to copy text contents at all
-Inconsistent with rest of iOS UI - make a spelling mistake on the last word, a correction should appear, hitting Send should Apply that correction, not cancel it
-UI Is slow overall. SMS do not refresh, even in official multitasking mode unless you go back to main SMS screen then back to conversation (doesn't refresh in jailbroken Backgrounder multitasking either)
-SMS screen will take forever if you have a lot of texts
-Google still hasn't learned to organize texts like iPhone's SMS app - by person, not by the weird data/conversation thing which is pretty flaky
-Inability to not page a phone with the app. Consequently, it's not clear what the ph # does in the app, because you can enter all kinds of bogus numbers. Not having a number locks out the rest of the app.
-Takes forever to load on non-3G. GV Mobile+ in comparison is faster, although GVM+'s UI is not so good

-No support for multiple accounts.
-No customization for push, or customization of anything that I can see. No availability of settings in web incarnation in app
Simple SMS equivalency. Is that asking a lot?