Corrected entry: I've always wondered how Kramer is able to live in a New York City/Manhattan apartment. The guy has no job, no prospects of getting a job, doesn't seem to have money in the bank (or at least enough of it to cover the costs of living in his apt) and yet can afford to live there. To the best of my knowledge it is never explained how he's able to afford it. [This is supposed to be one of the eternal mysteries of Kramer. In fact, Jerry and Elaine discuss how great it must be to be Kramer in one episode ("He meets all these beautiful women, he falls a**backwards into money...").]
Corrected entry: All of the cereal boxes on Jerry's shelf are alphabetized.
Correction: I know it gives this trivia on TBS Superstation, but if you'll look closely, it is not true. Often, Waffle Crisp is the first cereal in the row.
Corrected entry: Throughout the whole show, George Costanza is showed as being left-handed (eg. at the beginning of the episode titled "The Shoes", Jerry and George are writing "The Butler" script, and George can clearly be seen writing with his left hand). However, the actor himself is not, and you can spot some episodes (mostly in the first seasons) but a few in the last seasons as well, with him using his right hand for writing or eating, while in most of the show he's using his left-hand for everything.
Correction: Jason Alexander is left-handed. There are many pictures of him signing autographs with his left hand. There are also YouTube videos confirming his left-handedness.
However, in the episode "The Implant" Jerry says George can't make a move with his left hand because he is right-handed.
Corrected entry: Jason Alexander wore the same pair of blue Nike shoes for the whole series on every show (Jason gave this information in an interview, just after the series ended).
Correction: This can't be true because in the episode where they all go to India for Elaine's friend's wedding, George is wearing Timberland boots that make him a few inches taller.
Except at the end of that episode, "The Betrayal", it flashes to two years prior and George is with Susan and meets Jerry at The Cafe. He wouldn't have been wearing the Timberlands in that scene, so Jason Alexander could wear the blue Nike shoes in that scene and that would count.
Correction: As Jerry, George and Elaine point out numerous times, Kramer always seems to "fall ass-backwards into money" (think: frivolous law-suits, crazy inventions, gambling, and don't forget his "Coffee Table Book" deal). Slightly unrealistic, sure; but explained throughout the show.
In addition to these reasons, Kramer has a lot of friends and associates. He knows people who can do occasional favors for him, pay him to do the odd job/task, connect him with deals, etc.