What do you think of domaining?

This is basically where you buy a domain, then keep it for a while and sell it on for a huge profit (if you do it right).

The key is picking the right domain that is going to have massive value in the future, and then try and get it at the cheapest price possible.

Have you ever tried it?
What's the most you've earnt from a single domain?
What advice do you have for newbies?