Wirelessly posted (BlackBerry8100/4.5.0.102 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/107)Same thing happened to me last week IAH to YYZ on an RJ700.
I've had op-ups on two of my four transborder flights (not counting CRJs) this year.
Personally, I think they might be on the rise because AC is optimizing Y load factors, and they are selling out Y before J. So bump up a few Es/SEs and you can get seats for the standby Y passengers -- and everybody is happy. AC filled all the Y seats, didn't give up any J revenue, E/SEs are happy about the op-up, and standby passengers are happy to get on the flight.