When I'm browsing the active questions, it would be nice to see not only how long ago it was modified, but when it was originally asked. Here's a mock up
EDIT: I like seeing the creation date because I typically am not interested in really old threads. My observation is that most of the time (this is in general, not absolute), younger threads are modified because they're still in the process of being discussed. Older threads are modified to perform some kind of maintenance -- tag deletion/addition, or they just happen to be noticed by someone cleaning up old posts. So I don't like wasting time on the latter cases.