For PGP to really make use of MIME, it could use "multipart" types to separate the objects being encrypted and/or signed from the signatures and encrypted session keys associated with them.
No, this is WRONG. Take a look at the PEM-MIME Internet Draft. You *do not* want to separate the signature from the body of text being signed, since then you lose the delimiters of the signed message, and MIME can do anything with the data (like transfer tabs to spaces, etc.) This is BAD. If you keep the message and signature together, it will work better. MIME still does funky things, however, some times. Currently, you can easily use MIME as a transport mechanism for PGP messages. However currently there is no way to use PGP security for a MIME message. Hopefully we can take what the PEM-MIME effort has learned and apply that to PGP.. -derek