Don't forget to wipe (not just format) your HDD before sending it in! Techs have fun gathering statistics on private data found on HDDs.
For the HDD I donated over to my research group I used DBAN:
Darik's Boot And Nuke | Hard Drive Disk Wipe
For the HDD I just RMA'd to PcCyber/Samsung I used Linux's "badblocks" in destructive write mode.