After careful consideration for 3 months since I got my iPhone, I finally decided to jailbreak. Battery life was definitely one of my biggest concerns, as well as possibly screwing something up and not knowing how to fix it, or making the phone laggy.
After being jailbroken for a few weeks, I can confidently say that I have not noticed a decrease in battery life at all. I don't use the weather plugin for lockinfo, but use it for calendar alerts, notifications, etc and I love it. Lockinfo+bitesms is enough reason to jailbreak alone, they really are that great! I have not had any major performance issues since jailbreaking, but the springboard has crashed twice, just requiring a respring, nothing major. I have been pretty minimal with jb apps, and I plan on keeping it that way. I have installed a couple of themes and can now say that I don't miss anything from android any more ( ok, maybe I still miss google navigation, but that really is it now).