What exactly does the A-Bomb do? I've heard about it before but I've never played a character long enough to get it.
It tends to build up bad mojo so that around 200-300 hours on the same character animations will start to slow down - the onset is fairly sudden and noticeable. This can be very noticeable if you cast a spell on yourself as the residual swirls take a long time to dissapate. Your pause for a door transition will lengthen dramatically as well. Once it starts, quite soon the game becomes unplayable as the door animations will soon simply freeze.
On the PC, it can be fixed via a variety of utilities. I used to use a program called OAF, but once I installed Wrye Bash, I discovered it is much easier to quickly and simply fix using a feature of Wrye Bash. I only play PC and it is easy to fix; for those not on PC, I don't believe it can be fixed which means the end of the character in question. I'm no expert, but I think I got all that right.