Check your downloaded apps - one of them may be malfunctioning due to an incompatibility with the update. Best to uninstall them one at a time, most recent first, and see if there are is any improvement.
Widgets also can cause rapid battery drain especially those with RSS feeds or have frequent updates. Your screen backlight should be kept at a very low setting or on automatic. Believe it or not, having a black background (or dark) on your wallpaper will also conserve battery. The screen is a major energy consumer.
BTW, I have improved battery life since the upgrade - stunningly good, as a matter of fact! With more than 60 dl apps (not all running at the same time) and normal use, I'm still at 60-70 percent by day's end, having put a full charge in overnight. Battery life was miserable under 2.1 (30 percent after 2 hours), and better with Froyo (40 percent by day's end) but 340 has improved that even more.