I seriously doubt it's just the 2.80 update although when it happens shortly after, it's pretty easy to assign blame.
Did the update to a 40GB model, will do the update for a 60GB shortly.
The oven trick is the "easy" way to reflow the soldering on the motherboard. Can't say I recommend it, since it heats all the soldering joints on the board, but it seems to work in some cases.
The better way to reflow is to use a heat gun (preferably one with a temp gauge) on the specific parts that overheat and misalign (CPU, GPU, RAM).
And while that heatsink is off, clean off all the old thermal paste and use a better TIM like Arctic Silver 5.
There's an excellent guide here:
http://playstationlifestyle.net/forums/showthread.php?t=2376







