Here's an excerpt from a current article in 2+2's online magazine. I'd never thought about the value of table selection this way, but it makes a lot of sense. And I see a lot of players who play badly enough that they must lose significantly more than 2BB/100 hands.
Change No. 2: Improve game selection. So what's it worth to sit at a better table? Well, let's say your current table is a fairly strong table, but you're able to identify a table with two weaker players. Replacing two strong players who win 2BB/hr with two weak players who will lose 2BB/hr is a swing of 4 BB twice or 8 BB. If the rest of the table divides up those 8BB, that's worth 1 additional BB/hr to your winrate. Using PokerTracker, you can often datamine before or during play to find a table with two particularly weak players.
http://www.twoplustwo.com/magazine/current.../Soare0705.html