After upgrading to Lion, Reeder swipe up and swipe down gestures stopped working.
How do I fix them?
This problem is a known issue and has been fixed in recent versions.
However, it is not specific to Reeder and seems to also affect Twitter and other apps.
To work around it, hold ⌥ Option and swipe using the same count of fingers that you have set for Mission Control in Trackpad preference pane:
You can fix this (temporarily), but there's some plist hacking involved. I read on reeder's twitter feed about a solution to this problem.
The solution described at the linked address explains how to fix this problem in a couple of steps:
It's a bit hackish, but works pretty fine for me. The author of the post has also a different solution, but I don't really like that there's the option key involved.