I already do to an extent but come on, you can't tell me you use a completely unique password for EACH of the HUNDREDS of sites that use passwords? That just seems ridiculous, or maybe it's just me...
Between work and personal, roughly 130 password/account pairs.
I may be missing a few. I also don't believe in gratuitously creating accounts simply to make use of some site (information has value, including and often particularly, identifying information). I'll make use of BugMeNot and/or create throwaway accounts using Mailinator for one-offs.
Salt the password with characters from the url. Maybe your password is P4ssw0rd, so your HN password is Py4csosw0rd. I've been using this scheme for years, works great!