i kinda did a poor fan instan on a heatsink on my mobo.
but the fan is a little bent and it vibrates a little bit. but nothing bad enough that u can see it. u just hear it a little.
What heatsink was it mounted on? If it was mounted on the Northbridge, southbridge, ram, hard drives, you SHOULD be fine, as long as it's not moving the parts. If it's the CPU heatsink, I strongly advise you buy a new fan.
Fans are cheap. You should replace it. If it's vibrating then it's probably slightly out of balance. And if it's out-of-balance then there's a possibility that one or more of the fan blades can break. And if a blade get's thrown at the right component damage can occur.