How do I get three finger gestures working again in Twitter for Mac after installing Lion?
This annoyed me too, and it doesn't seem the solution is entirely satisfying — we'll just have to hope that Twitter for Mac gets updated soon to be better compatible with Lion.

If you have "Swipe between pages" set to "Swipe left or right with three fingers" or "Swipe with two or three fingers", then left/right three-finger swipe gestures will work in Twitter.

If you have Mission Control &amp; App Exposé set to "Swipe up/down with three fingers", then you can hold ⌥ Option to use up/down three-finger swipe gestures with Twitter. (I'm not sure why, but if you have these set to 4-finger swipes, it doesn't seem 3-finger swipes work at all in Twitter.)