I've experienced (PS3) a lot of glitches online but none in splitscreen or singleplayer. I've seen people join my online game at level 0 when they are really 30+. One guy told me that when I got into my vehicle it said I was at his level of 28 when I'm actually 31. I've seen players run through gates/fences. Another friend on my friends list lost all their weapons for a short period of time and had to disconnect and reconnect online to fix it. 
 
The Friends list in my game screen has people who haven't bought the game, I read that only people who have installed the game will pop up on the friends list but this is another bug that EVERYONE has experienced.
 
There are an ENORMOUS amount of bugs on the PS3. Gearbox just announced a patch for the 360 only.
 
http://xbox360.ign.com/articles/104/1040589p1.html
 
October 29, 2009 - Enjoying 
Borderlands, but coming across way too many bugs and glitches? Help is on the way! 
 
Developer 
Gearbox Software will be 
releasing an update Thursday October 30th at 2 A.M. CST for the Xbox 360 version of Borderlands. Gearbox also states they'll eventually release a patch for the PC and PlayStation 3 versions as well. 
 
 
Fixed a bug which caused players and other things in the world to appear incorrectly on clients in networked games 
 
fixed a bug in which players gibbed in arena combat disappeared 
 
fixed a bug which caused the dollars counter to spin continuously 
 
fixed a bug that caused the digger elevator to be unusable after completing the Find Tannis mission 
 
Weapon mapping to the D-pad should no longer reverse left and right 
 
various localization and other text and tooltip corrections 
 
The introductory quests with CL4P-TP should now always progress properly all the time 
 
Lilith's Phase Strike ability now works as intended 
 
Load times have been improved 
 
I have played over 20 hours online and have been able to overlook these bugs for the most part because I love this game and am addicted to it but it's rediculous. The 360 has NONE of these problems the PS3 has and the bugs they mention for the 360. My 2 friends who play the 360 version have never experienced any of these bugs.