Chad,
I was a sketchpad user for YEARS, but I made the switch to GeoGebra
just because it was FREE, so my students could use it at home. The
things in the new version of sketchpad is just "catching up" on the
part of GSP...GeoGebra has been doing that stuff since the beginning.
It really is like an 83 or 84 or Nspire. THis summer, the developers
are making improvements the spreadsheet, are adding more CAS
functionality, and by 2011 school year, a 3D component. And all FREE!