Ok, so that's what I can add non-off-topic to your problem:
- It is not overclocking problem. It's just not the case here, believe me.
- You probably have some daemon running in the background. If you are curious, you can read about what a deamon is here: http://en.wikipedia.org/wiki/Daemon_%28computing%29
- QUESTION: You could run on your device:
Note that / is different character, than \. And also it is "ps" followed by space, followed by "-A" followed by space, followed by ">", followed by space, followed by "/home/user/MyDocs/runningprocesses.txt" (I remember you might encounter problems typing commands in terminal, last time you forgot important part of command I asked you to type ). It will create a file on your N900 storage, so when you connect your N900 to your computer and open it from your computer, you should see file "runningprocesses.txt" in it's main directory. Please attach it here. If you cannot see or find this file, read my instruction again and repeat the whole process, if it's still not there - you are making a mistake somewhere and please don't ask here why it's not working and you cannot see any file like this.
- I can be wrong (and probably am), but if I were you, I would try searching CSSU thread for similar reports of battery drainage (if you have CSSU installed), because it may be the problem (just may, please don't be mad at me CSSU devs pretty please ).
- From my own experience with my phone (your experience may differ): it may be tracker or thumbnailer indexing crazy like there is no tommorow.
- QUESTION: Did you install some extra protocols for contacts and conversations? I'm again only just guessing, but I remember that (especially msn protocols) some of them were in the past (LOL, I tried them ~1.5 year ago so it might have changed) trying to connect to the Internet constantly and constantly running in the background. It may also happen if you have Pidgin installed and turned on (you know that to turn this baby off you need to actually select "Quit" from it's app menu, because just closing the window makes it stay turned on for eternity?)

I didn't mean to be rude writing this post, so also please don't feel offended, I was trying to be nice and explain everything

Edit: Your attitude towards JohnLF (he was trying to help in at least one other thread and you didn't even listen to him and didn't answer him and now you offend him and call him "sh*t") makes me a sad panda That's just wrong...