You know that's actually a lot (a very large lot) better than having the same password for multiple sites (like for example the common three password security levels strategy).

A bruteforcer might find a hash collision, but it's not likely to find the entire string {password}ubuntuforums.org unless it is actively looking for that string.

Granted ofcourse that all websites you do this on store their passwords securely.. if not then you are right, it is a terrible idea :P