Version:           1.8.2 (using KDE KDE 3.4.2)
Installed from:    Compiled From Sources
Compiler:          gcc 3.3.4 
OS:                Linux

KMail has been hanging badly recently, for roughly 10 - 20 seconds per email whenever I fetch new mail, delete mail, move mails to different folders, or send mail. As you can imagine, this is a severe impediment to working with email, and I was on the verge of changing to another email client because of it.

It started happening while I had KDE 3.4.1 installed, and has continued with 3.4.2. It turns out that it is the existence of search folders which causes it. When I deleted my search folders, kmail started responding normally again.

There are other reports about this referring to "high system load", at http://lists.kde.org/?l=kdepim-users&m=112471194622458&w=2