LAMP hosting solution for web applications and sites I build for my clients.
Also runs as a backup MX for when my ADSL is down. (I am resting my foot against my primary MX

)
Sometimes fire up Squid so that I can proxy out from the USA when a) I think I'm having routing problems and b) to see how things look different when GeoURL is in use. Also allows me to bypass my ISPs wretched transparent proxy which has a habit of doing some really weird caching sometimes.
Second Linode is redundant LAMP server for when the Big One hits Fremont
As this server is pretty well in sync with the primary, I use it for pre-deployment testing of new code for client apps. (On the grounds that the client can play with it here - they can't if it's just running on my laptop.)
Tertiary MX.
Also runs a couple of Mailman lists for a client.
Both Linodes run Gentoo, but with LAMP components all hand-crafted rather than standard ebuilds.