this situation is 100% repeatable on my N900 with CSSU, with or without overclocking.
how to reboot:
1. connect to the wifi
2. open cutetube-qml. you have to have a youtube account and be signed in.
3. exit cutetube-qml
4. immediately (~1 second) after turn your wifi off with wifi switcher.
5. phone reboots

the phone will not reboot if:
- you don't have a youtube account (not signed in with cutetube-qml) or
- wait ~5 seconds after closing cutetube-qml and then turn wifi off.

Versions of the software:
cutetube-qml 0.9.4 (the same was with .3 and .2; don't know for previous versions)
wifi switcher 0.0.9

Can anybody else reproduce this behavior?