http://www.gmbuypower.com has a terrific payment estimate tool that will let you compare buying, leasing, and smart buy.
2 year smart buy residual of .73 makes for a pretty good deal, although 8.75% interest rate was best my dealer would do.
Best way to use tool is find a vehicle using inventory search, then use estimate payment under GMAC financing link.
It is pretty fun to go into the dealer with a printout of this info and watch them scramble after their first numbers come back so far off.
Good luck.