It doesn't ever really pay to wait too long. At this point, though, I'd wait until after Macworld Expo and the "Stevenote" presentation, just in case. It wouldn't be unheard of to get a surprise release of something cool, but I wouldn't get my hopes up for anything big in the iMac line anytime soon. If anything, I'd suspect the regular MacBook line might get revamped a little bit (styling wise), but the rest of the lineup is pretty new.