The number of times I've popped up filemon to see Chrome, Safari, or some "Google Safe Browsing" thing thrashing my disk in the last 6 months is kind of a lot.
I usually just kill the offending process. For instance, I think Safari uses some variety of sqlite for its web cache, and once a day it just thrashes for a minute. I mean a full minute during which my computer is basically useless. I have a darned fast RAID on this machine, and it still is the rudest thing in the world.
I'm accusing sqlite. When you have sqlite and it's free, everything looks like an ACID database.
Let me be specific: you do not need ACID for your cache. You can do writeback. You don't need tiny blocks that make my disk seek too much. You can make a big append-only file, and you can tolerate some fragmentation. Be sloppy. Use 2x the space you need.