This is a suggestion for Google, Bing, and anyone else still attempting to compete in the search engine space:

Provide a user configuration option to exclude domains search results. 

For almost any information domain I might care to search, certain sites have SEO'd themselves into high positions on the search engine results, but I know I don't want to go to those sites.  For example, experts-exchange.com frequently comes up high on the list when I'm searching for technical information.  Or about.com comes up high when I search for almost anything.  But the experts-exchange information is subscription-only and about.com information is mostly a shill for advertisers.  I'd like to be able to explicitly exclude these from every search. 

The search engine providers have approached this so far by being secretive about their algorithms.  But companies like the ones I mentioned employ smart people who spend their work days evaluating and gaming those algorithms.  The current approach isn't working.

And the domains I'd like to exclude vary with the information domain I'm searching for.  Experts-exchange won't come up when I'm looking for recipes, but there are a whole raft of sites in that domain as well.

In fact, if I were Google or Microsoft I'd allow users to create an exclude list and mine their users' lists to lower these sites on their rankings.  Of course the SEO guys will try to game that too, to lower their competitor's results.

The game never ends.