Why is Chrome getting so slow when file vault is enabled?
I've solved this problem by moving my Chrome cache outside of my home folder as follows:

Closed chrome. Then in Terminal:


cd Library/Application\ Support
sudo mkdir -p /local/myusername/
sudo chown myusername:_lpoperator /local/myusername/
mv Google /local/myusername/
ln -s /local/myusername/Google


Update: I'm not entirely clear why this speeds things up again, since, as was noted in the comments, File Vault 2 actually does encrypt the entire disk, not just the home folder. But it does seem to work nonetheless.