Lion has been fine so far on my MBP - apps/printing is fine - the dealbreaker for me is i1 doesn't run (requires rosetta, cost of upgrade is pretty steep).
Love the new mail.app, although the address book appearance is just stooopid! Another aspect is the hidden scrollbars - I thought i'd hate them, but i love how clean things are without 'em.
Lion Server's SMB (windows shares) implementation is causing me some grief - seems to work fine on the Lion Client, but having problems seeing SMB shares hosted on Lion......
Jeff, I also have some major issues with the App store
On one hand I can appreciate the cost savings, on the other, they *really* need to have human beings available to talk to (I actually have my state's Attorney General looking into this - they also have an issue with that phone number appearing on your bankcard statement going to a recording).