My old Treo 600 used to last 9-10 days of average use on a single charge. A few SMS per day, 1 or 2 calls per week, some games...

My N900 lasts about 2 days of the same use on a single charge. It's only when I turn on WiFi or GPS when the real drain starts. Probably best exemplified by my second N900 that I bought on eBay 3 weeks ago, charged once and left alone. It ran out of juice just now.