My donor card says I hadn't given since December 2000, which seems improbable. My Palm had a record of my going in March 2001, and I guess it's possible (if a bit embarrassing) that it's been two years! I coulda sworn I gave blood that summer or fall.
The good news is that I won't have to wait long after getting back from Scotland, as I thought I would. I'm probably getting close to the point that I've spent a total of over three months outside the US since 1980 (a warning flag), but definitely not three months in the UK (automatic ineligibility to give blood).
I'm at about two and a half gallons, and will try to get back onto a regular schedule.