Southern California Edison has been offering rebates for both two-speed pumps and variable speed pumps. Starting sometime in 2010, it may discontinue rebates for two-speed pumps, and issue them only for variable speed pumps.
Meanwhile, other states are following California’s lead and are either considering or have already adopted energy-efficiency regulations similar to Title-20.
In my opinion, variable speed pumps are not ready for mainstream use. They are still too complicated and buggy in terms of nuisance alarms and the frequent need to reset the processor to clear such alarms.
I see a wide open need for a ultra-efficient motor that is as simple as a two-speed. So far it looks like Century New E Plus Centurion fits the bill. See my youtube video for an installation and energy saving calculations.