Hi
sonofabit: Check this out in x-term and post a powertop.txt content.

sleep 60 && powertop >> powertop.txt

Wikiwide: I had similar problem but in my case, n900 was turning off every time the red led and notification of low battery state appeared. After some researching I found out that power amlifier ( gazoo ) was the culprit. It was spontaneously dropping down the voltage below 3.2v what was causing shuting down. Puting a sim card above gazoo helped. It can be also related to no telephony problem, because when I stoped bme and voltage dropped down the "no sim card" icon appeared
Did you have problem any of this problems ?