I first bought fallout 3 on ps3 because i didn't know it was available on pc, but i didn't experience any lag with it. Then again... i didn't get a lot past first seeing megatron before i bought the pc version.
About a month before TES IV Oblivion was released i just got my hands on a new Pc who was able to run the game on the highest settings without any lag or visual delays, it was perfection. I threw it away because it was getting quite old and wasn't able to play games as it used to... I'm getting a new one a few months before Skyrim is released again and i'm sure it'll run it perfectly
.
Honestly with consoles i don't think there will be any lag in them. The game's graphics usually get stripped until the game can run it perfectly. But if you play for several hours in a row your console might be getting a bit too hot which usually results in lag. At least that's what happened when i was playing Fable III. It acctually got so hot it melted the cd... Bye xbox and Fable III :'(
As far as low Fps or any other type of computer lag goes it totally ruins gaming for me... Oblivion ran perfectly, but it still crashed every few hours which isn't so bad, but if you get the same delay every minute or so i wouldn't even bother playing it... Best thing i can suggest is simply get a decent Pc, and play it on that. The experience will be so much better then.