I still have my 60GB phat boy, but I rarely turn it on to prolong its life because my slim is in use nearly every day for hours.
When I got Uncharted 3, it wouldn't load on my slim -- it took sometimes upwards of twenty tries to get the disc to be recognized and then all was fine! All other CDs, DVDs, and blu-rays and games would play fine.
After one exchange and trying a friend's copy of U3, I figured the issue was limited only to 50GB blu-rays because Avatar also wouldn't load up on the slim.
From what I've read, this seems to point to the blu-ray laser wearing out?
I tried the Maxell Blu-ray cleaner (it is a DVD with two holes in it, it vacuums dust away from the laser lens) and it helped for some disks, but it did not eliminate the problem.
So I've bought a replacement laser for about $30 on e-bay and it arrives this week hopefully. Has anyone else gone through this experience?