I have a slim version PS3 I got a year ago and it runs Skyrim just fine. I have no big issues to complain about as far as performance goes. I guess I am one of the lucky ones.
Oh and I also play Skyrim for long stretches of time and I still get a smooth performance.
You know its funny that I also am trying to get a good friend of mine Skyrim and he is also on the PS3. Its a sad thing that we have to actually worry about the PS3's performance issues.