don't know if it's directly relevant or not, but during a recent walk (battery fully charged before setting off) I had tracking enabled on maep,with nokia messaging running for push gmail, the built in media player for music, with occasional use of the camera plus the odd SMS. I stopped media player after a while, and later on when I stopped for a coffee I realised the n900 had switched itself off. It wa totally dead & unresponsive - it would not power on again until after I took out the battery - when I put it back in, the phone booted up fine again.

That was the first time I'd used the tracking feature, so I assumed it was probably a bit buggy, but perhaps my lock up was the same as your 'death spiral'? I tred to reproduce the problem but I walked for another hour with tracking+music+push email+camera+calls/SMS+email send/receive (I even did a bit of youTube to stress it!) and it refused to break again. Total duration of that walk ewas about 3 hours, the lockup happened after ~1 hour. As far as I'm aware it didn't hang in response to any action by me, it just died in the background. My n900 hasn't got much from extras-testing/devel and has never needed a battery removal before or since.