Maybe it's my PS3 (80GB Old Style) but I'm getting horrible graphic artifacts when playing. Not just specs / white dots but artifacts and flickers in the environment. At first I thought bullets all had tracers on them but then I realized that that environment effects were also getting weird streaking. 
Anyone experience something like this? I'm thinking that my unit it's on the way out (it overheats a lot, randomly reboots during a movie, etc) and I should just bite the bullet and replace it but if there's a fix, it'd be nice to delay the inevitable.

Yeah I haven't heard of any glitches graphically with it so far, but it definitely sounds like it might be the hardware causing the problem though.
 definitely sorta sounds like it might be time to move on from it...

i saw someone complaining about the graphics being messed up for the Retro Map pack.  Not exactly sure why.  The person was saying everything was extremely blurry and they couldn't see.  They re-downloaded it and said it was fine.
 
For me, on one of the maps the lighting was being funky for me but it was not on a DLC map.  Like the lens flare was so intense I couldn't even see.  I figured it was part of the map but I never noticed it before that or after.  I'm on a Slim PS3 so probably nothing to do with your PS3 itself ya?

I've had sound and freezing problems.   I think the sound effects issues were resolved in the first patch.  So far my PS3's frozen 3 times playing Killzone 3, once during gameplay (someone had just killed me) and twice during loading / connecting screens between  rounds.

I had a real graphics problem in multiplayer last night. Only time though, it was on a retro map I think.

I'm running on an 80 gig and it's all good for me.

Mine's had a lot of emotional problems for awhile now so this might just be the last straw... It'd freeze constantly during Heavy Rain and show weird artifacts during GoW3

I've only had audio problems. One of Jammer's lines "I'm coming up on your right" literally got bugged and all she was doing was "I'm coming up on your righ-I'm coming up on your righ-I'm coming up on your righ" etc

i noticed one glitch in the campaign. i was wondering around and found it though, so it didnt affect the experience at all. i was able to see right through a wall. 

" Mine's had a lot of emotional problems for awhile now so this might just be the last straw... It'd freeze constantly during Heavy Rain and show weird artifacts during GoW3 "

time to get a new ps3!  do you have enough space for your ps3 to breathe?

"I've only had audio problems. One of Jammer's lines "I'm coming up on your right" literally got bugged and all she was doing was "I'm coming up on your righ-I'm coming up on your righ-I'm coming up on your righ" etc "

Sounds like your GPU might be dying.