Went from linux to WHS
Actually I went from a headless debian server (bubba One from excito.com) to a MediaSmart EX490 3 months ago which I picked up on a cashback offer, making it quite good value.
I originally used the debian server as a backup for the two laptops in the house (Macbook, Windows 7) and a media server for music and photos. It all worked find until EDF fried it by blipping the neighbourhood's power supply one afternoon, but was very low on free space.
The new server (with 3 2TB drives installed) acts as the backup server (including TimeMachine and Windows 7 backups as well as data only backups), music server, photo server, and DVD store (we use a Popcorn Hour A110 as a movie jukebox for 300+ ripped DVDs).
This is all backed up to a 4.5 TB NAS (belt and braces approach), with the laptop image backups protected using WHS replication).
Essentially I am using the WHS as a NAS on steroids, but at the price point I purchased it at it worked out better value than a dedicated NAS with the feature set (and room for expansion) that we required.