Had an interesting experience yesterday. Found out at Skyclub my ATL to SAN flight was oversold by a couple. Went to gate early and inquired (first one to do so). Was offered $500 Delta bucks and seat on flight 4 hours later if they ended up needing me. They did ask for additional volunteers and the price went up to $600. Eventually the extra folks were told to board and were given some drink coupons for their trouble.
A short while later and after everyone had boarded they said it didn't look like they'd need me anyway but gave me a cert for $150 Delta bucks for my trouble (first I've ever seen that). Got onto the plane, stored my bag and right after sitting down they came back onboard and asked if I was still interested (yes) so got back off the plane and traded in my $150 delta bucks cert for a $600 one.
I've done the VDB previously (highest was $400 DB before this) but have never been given a cert for waiting around and not being needed. Not sure if this is a new policy or a one off but thought it was pretty cool.