Exactly the same problem.

after using n900 for 5 minutes, it become very warm.

the keyboard, the back pack (battery) is just hot

then put it away for 20 minutes, it become cool.

I use Conky to check and all is normal.

CPU usage is only 2 percent.

Is it related to the summer ?

I used PR1.2 before and no such problem.

I had just reflashed ROM and EMMC and only a few apps installed now. The problem come yesterday.

I think it is not OS related.

This thread should be put on N900 section.
can some guy from NOKIA take a look on this issue ?