Im new to the Iphone and Jailbreaking so..
I'm learning...Just miss my JB apps and themes
Best thing to do is as soon as Apple releases a new firmware update, look at it's features. If it doesn't have anything big in it, ignore it. If it has big features (AirPlay, the whole 4.0 update, etc), keep an eye on this forum for any posts with the firmware version number in the title for discussions on the jailbreak ETA.
Also, most of the repositories (the places that Cydia pulls the lists of apps from) get hammered during the first 24-48 hours of a big update jailbreak (4.0, 4.1, 4.2, 4.3), so it's best to hold off just for a short while letting the frenzy cool down a bit.