[plt-scheme] Contracts performance

I'm trying to get my head around the performance overhead associated
with contracts.  I noticed in the manual it talks about the space
overhead between returning any vs. any/c in a tail-call recursive
function.  Are there some other common "gotchas"?  How about (listof
any) and related contracts?  Is that O(1) or O(n)?

Furthermore, if you turn off debugging information, does contract
checking go away as well?

--Mark