With the new talent trees and the challenges of leveling, I've had to adjust my talents several times. On my warlock, I did a post-2.0 build before the expansion pack that was very heavy demonology, a leveling build that was heavy affliction, then I tried multiple builds for post-70, settling on a hybrid 40/0/21 build similar to my old raiding build.
Fortunately I'd had my old raiding spec for a very very long time, and my cost to switch everything now is up to just 30G. How many times have you unlearned your talents lately? What's your re-spec cost up to?