There is a way to stop the disc from loading on boot, press your PS button to turn on your PS3 and when the orchestra plays and you see the waves just hold up on the controller. The icon will scroll to the top of the screen and the game will not boot.
I do this a lot as I leave my resistance game in my ps3 24/7 and I play demos alot.
Mines frozen twice in Bluray plackback of Taladega Nights on 1.32, but I upgraded my firmware to 1.51 (I use my PSP for homebrew) and moved my PS3 from my thick carpet to a stand and I've had no problems since. *crosses fingers*
As far as i can remember my ps3 has frozen twice once on the f1 demo just before loading the race and once on call of duty 3 as it was saving my game luckily my save was ok but i had to reset my ps3 to carry on from where it saved.
and for the signing in issue i've had that happen once the way i got round it was i made another user account and logged onto the new one then back out into my account then it signed straight back in as it should do.