Forgive the example: I had a passing interest in Coldplay for a while, mostly stemming from their Apple commercial (I am a huge Apple freak).
I looked them up on Youtube, looking for some live concert footage. Well, I found some. And it was boring. Sounded great, but the guys just...kinda...stood there. Or sat there.
This might not be fair of me, maybe they were just having an off day, but have you ever been disappointed by famous artists who turn out to be less-then-stellar live? Who?