Don't know what I was thinking when I wrote that firstbits could be used for a brainwallet. Firstbits is for addresses, not private keys, so obviously it wouldn't be of any use. Duh.
I thought you meant that you if have a brain wallet like the one generated by "correct horse battery staple", which, if you use the default settings at brainwallet.org, corresponds to the address 1JwSSubhmg6iPtRjtyqhUYYH7bZg3Lfy1T; then you could accept payments or send yourself some money by remembering only the firstbits, which could be 1JwSS, quite short.
This way you could keep all the stuff you need for using Bitcoin in your head. You obviously remember your brain wallet's passphrase, so you can access your funds if you need; with firstbits you can also quite easily remember your wallet's address, memorizing the full address would be unnecessary (it's difficult, many people probably would not want to do it).
This is exactly what I have been doing. I memorized all the firstbits of the addresses for my brainwallets. That way everything important was stored in my head. I certainly don't want to use brainwallet.org on some random computer to figure out my address. For right now, I just keep links to the addresses of my brainwallets on a file on my website.
