I’ve been running 10.6.1 since the update was available, and been running SpamSieve for a couple years. My last login to the forum says 11-1-07 so you can get an idea how trouble-free things have been for me.
However, this morning I started Mail and noticed that my macbook became very very sluggish. After a bit of investigating I noticed that once SpamSieve starts Mail starts consuming as much memory as it can and the machine swaps continuously. iStat showed page-outs climbing rapidly and disk writes at 30+MB/s.
I cleared the font caches, booted into safe mode, used MainMenu to clean out everything it could, all the usual tricks I try, but no help.
I reset my corpus, history, cleaned some of the white and block list rules in SpamSieve; no luck.
After about an hour I found that Mail would operate properly (and not swap) by disabling the SpamSieve rule in Mail. I even removed my mail accounts and created them with new names thinking something was more seriously corrupted within mail. Still no luck.