… and quietly rake in some niche profits.

YouTube is quite a phenomenon, but as yet has not made a profit. Quite likely making $$ are the niche clones like YouPorn.com & Godtube.com

Homework:

1) Create a list of broad niches that have loyal followers (porn, religion, conspiracy, WWF)
2) Watch for when a general website becomes a hit
3) Clone it, niche it, $$ it