I like to make all my wallets brain wallets and import them into my MultiBit client.
I think this somewhat defeats the point of having a brainwallet in the first place. If you are going to make a brain wallet then you should keep it in your brain. By making a brainwallet, you are giving up one portion of security in exchange for another. You are giving up entropy in your private key in exchange for the possibility of your private keys being stolen by malware being generally removed.
there is a trade off, that's true, but not the one you say necessarily. if done right the b.w. has high entropy.
With a b.w. you're getting protection from theft or destruction due to physical access to hardware or paper...plus you get greater access/portability, in exchange for the risks of physical attacks and coercion on your person, human memory failure, and possible difficulty in transferring the wealth to next of kin.