Goods and Bads of each Firmware (read, new people!)
1.0:
Pros: Homebrew allowed without KXploit
Cons: Only sold commercially in Japan
1.5:
Pros: Allows homebrew with KXploit
Cons: Sony wants it updated NOW
1.51:
Pros: None
Cons: No homebrew allowed
1.52:
Pros: UMD Music can be played
Cons: No homebrew allowed
2.0:
Pros: Web browser, extra video and music controls, picture teleport, custom backgrounds
Cons: DEFINATELY no homebrew
Hopefully this will clear up the endless "What can 1.51 do" and "I wanna upgrade wat are the features" threads.