i don’t know if the eris has the same 1500aH battery as the hero, but i noticed that if you install locale or something to manage wifi and gps signals, it cuts way back on battery… there is an app called drain-o-meter or something that will take samples and return teh apps that take the most battery… same with the battery apps that give detailed info…
after a week or so of configuring my battery life is good for over 12 or 16 hours a day… day 1 of using the phone it was dead after about 3 hours of use lol
personally the gmail integration is money for me… and it’s layout and management of corporate accounts is stellar compared to blackberries limited management of email accounts… although i still have a blackberry as backup since the battery on it will last at least 3 days without dying (8830).