Is the input lag issue on SF/Marvel on PS3 compared to 360 something that is across the board, or unique to Capcom games?
SSF4 and MvC3 issues on the PS3 are different for my understanding.
SSF4 on the PS3 runs with 1 or 2 frames of delay. That means the game runs at 59 or 58 frames per second. Well is not like it really runs at that speed, it just "feels" like it does, if that makes sense. In reality it doesn't affect the game hugely, it's noticeable ones you jump from 360 to PS3 or viceversa. But you get used to it fast and is easy to just focus on the strict frame links combos when you start doing it. But in the end the 360 version runs always at 60fps and by default it's considerate "closer" to the arcade release, but that doesn't mean it's perfect.
In MvC3 is different, both games run exactly at the same speed. The only thing is that the PS3 has V-Sync and it causes the game to drop frames when there is a lot of chaos on the screen. Meanwhile the 360 version doesn't use V-sync, so there is no frame drops, but you will see screen tearing when there is a lot of chaos. I don't see MvC3 frame drops affecting the gameplay at all, because it only happens when you are doing Hypers and not while doing combos. So you won't see frame drops while pulling out frame specific combos, hence not affecting the gameplay.
But the PS3 versions of both games are 100% playable and is just a small nitpick that can be easily solved by adapting. Besides in a tournament there is a HUGE chance you will be dropping combos, but not because of the system you play, but because of the pressure you feel during the tournament and I bet that will happen in either PS3 or 360.