I had a shot on Guitar Hero 1 after only playing 3 for a month or so, and I've lost any skill I used to have. The controller is a bit fucked, so there's a technique to using it properly, you've got to know that some buttons don't work if you don't press them right, and the whammy bar only works at certain angles, and I was totally unable to do it.
Ever seen that bit in "Back to the Future" where Marty's picture starts fading when he's on stage, and he's unable to play? It was a bit like that, but instead of ceasing to exist, I only got 4 stars on Ziggy Stardust instead of 5.