Probably like most of everyone else, my starting point included downloading the official bitcoin client, creating a new wallet.

However, i immediately noticed two things:

 1) i choose a password (a lil security? yeah sure) but when i close and re-open the app, no prompt is given and the wallet is opened...
  ... so, i guess my pass got stored somewhere 

 2) No wallet export/import. Seriously, this should be a MUST.
    Yeah, i know the risks, i'll encrypt the data myself (GPG, whatever)


Ok, other wallet software exists, but each has it's own format as well... 


My question is, what exactly is the essential data a wallet must contain, and why?
I've read https://en.bitcoin.it/wiki/Wallet but information is scarce


Any linkage is appreciated