Version:           1.6.2 (using KDE 3.2.2, Gentoo)
Compiler:          gcc version 3.3.2 20031218 (Gentoo Linux 3.3.2-r5, propolice-3.3-7)
OS:          Linux (i686) release 2.6.5-gentoo-r1

I use PGP via the external GnuPG tool and verifying signatures always takes a jiffy on my box. It's not as bad as spam filters for incoming mail but it can be a bit annoying if you walk through your unread mail via the keyboard and KMail tend to take a small break for each signed mail. But one can live with it.

A few days ago I configured my GnuPG to automatically retrieve unknown keys from the keyserver. And depending on the responsiveness of the server this can get very annoying now. The worst thing which can happen is an unknown key which is not known by the server neither. This will stall KMail for about 30 seconds.

So I suggest the following: Instead of calling gpg and waiting for its response, start it in the background and refresh the display when the results come in. While the tool is running, the signature status border around the message could be held in grey or something and the text changes as soon as the status is clear.

This is all partly related to the dreaded bug 41514, I guess it has to/should be solved in a similar manner.