I was trying to figure out how to make the Vegas transitions a little less abrupt looking (linear) by setting keyframes in the transition to smooth. But, it didn't seem to make much difference in the interpolation used by the transition. It was always linear looking. But, I stumbled across "Transition Progress Envelopes" in the help section.

Right-click a transition on the timeline and choose "Insert/Remove Envelope - Transition Progress." If you just leave the envelope as-is you will have a smooth interpolation at the beginning and ending of the transition, but if you start adding keyframes to the envelope you can get some very interesting results...

Leave it to Vegas. There's always something interesting lurking beneath the hood ;-)

Jim