In case I forget to fn-F1 it when closing the lid and stick it in my bag: is there any way to make it hibernate (save to disk and sleep) if the internal temp gets high?

Mike

No, not without scripting something for cron.

This is something I'm already considering for the next major release based on a previous users request.

One possible solution for now would be to change the setting in the gnome power manager to hibernate when the lid is closed while on battery.