Of course since blowfish is a symetric algorithm you'd need to arrange a secure channel for exchanging keys (say by using a public key algorithm like El Gamal or RSA). And you'd have to come up with a message format. Then to avoid tampering you'd want a MAC. And . . . and . . . and . . . . At which time you'd have probably reimplemented something resembling PGP.

Just remember, doing crypto correctly is hard even for people that know what they're doing. Going with something standard that's been gone over by many eyeballs is more than likely going to be more secure than rolling your own.