I have been wanting to participate in this discussion, and am now happily past the newbie speedbump. 

I like the concept of deterministic wallets, and am thinking of an approach that lets me create deterministic and encrypted paper wallets.

It starts with a brainwallet created at bitaddress.org with a 230+ bit entropy passphrase.  I then encrypt the private key at bit2factor.org which implements BIP38 to create an encrypted private key.  For this encryption, I use a different 230+ bit entropy passhprase.  I then use the encrypted private keys as the successive brainwallet passphrases to create more encrypted private keys in a deterministic manner.

I have read this full post and others like it, and am aware of the need for high entropy passphrases.  I can use even higher entropy passphrases than what I am thinking of, and I can reliably re-create the passphrases when I need to.  But I am interested in knowing how much entropy bitcoin passphrases can handle.

My questions are:
1) what is the limit for the number of characters a passphrase can have to create a private key at bitaddress.org?
2) what is the limit for the number of characters a passphrase can have to encrypt a private key at bit2factor.org for the BIP38 implementation?

Thanks.