I have done thorough testing about my problem of battery dying in less than 7 hours of idle. In my case the problem is triggered by connecting to Wi-Fi and no matter if you immediately disconnect or set the phone to offline mode or whatever, the bug triggered won't go away. Only reboot will help.

Without using Wi-Fi (for me the phone searching for Wi-Fi while I manually initiate 3G connection doesn't trigger the bug. I have set the phone not to search for Wi-Fi on its own.) I get 9.1 days of idle time. See more info in the actual posting about it:
http://talk.maemo.org/showthread.php?p=418901