I have exactly the same problem. It was introduced after a kernel upgrade from 2.6.8 to 2.6.19.2 under Debian Sarge.
Under Sarge, I had one encrypted partition, which had these
problems. Unencrypted partitions were ok. With the older kernel, I did not have this problem.

I am now using Debian Etch with the standard 2.6.18 kernel. The problem persists. I now have a fully encrypted system with a dm-mapped partitioning inside an encrypted partition.

This is aweful -- the computer is quite unusable for interactive tasks during this and my load is at about 14 (from *one* single cp from DVD to disk!).

NablaOperator - as your post was about a different system to the one in the Slackware forum (and the one in Slackware was 3+ years old), I have moved your post to the Debian forum and named it "Sarge System Unusable After Kernel Upgrade".