It's taking a long-ass time to save data, at first I thought it was my connection acting up when downloading stuff since it took AGES to download a 300MB file (it takes me 30 minutes or so) and when I changed to save stuff on my USB stick it was normal speed.
Then I was playing Rock Band and it took the game several seconds to load the songs properly in the menu and then to play them. Copied a few to my USB and they took no time to be read and played.
Well, I can't complain, I got it from MS itself in a 'get a 20GB refurbished HDD for $25!' thing they had around the time I bought the Xbox in December 2008. For a refurb it lasted pretty well.
