Well, current MPG info listed on toyota.com is 48 city/45 highway/46 combined for the Prius so you can probably guess hybrids have the largest advantage in the city. Hybrids generally are redesigned to have a much lower drag coefficient and among other tweaks to increase MPG.

If you seach for "diesel vs hybrid", you probably come up with articles claiming diesel can match or beat hybrids on the highway. :)

Seems like I may have to wait until 2011 (Dec. of 2010) for clean diesel to be availible at every pump... (http://www.clean-diesel.org/faqs.html/). Damn EPA! :p

I could try to get a used Jetta TDI in the meantime possibly or wait for improved Jetta TDI (is being delayed). :D