It seems that the launch of last.fm's new site has strangely broken the older API that LastGraph uses. I knew I was going to have to update to the new API, but I didn't think it would be this soon!
For the two eagle-eyed people who've contacted me about this, well done - I'm working on a fix now (the precise problem is that the old API now always returns the last week's data, no matter when you ask for, hence the very flat graphs).
Update: After a quick three minute URL change, it seems the new one is ALSO broken, and other things such as the lovely Last.fm Spiral are broken too. Time to go make sure they know about this at last.fm HQ.