Thanks for the replies, I must say the isolation transformer always leaves me a bit on edge. That stray USB cable on the bench with it's grounded connector bumping the DUT, stupid stuff like that. I have a Tek 2465B and a Rigol DS2302A, the Tek is a bit nicer to use with the differential probe trick, however from experience I don't care for that method on either scope.
I've also been looking at rolling my own differential probe design (like many others). It's easy enough to get usable bandwidth, getting that flat is a little more difficult. I may just spend the cash and get the Instrance 100 Mhz model. Worse case it sucks and I can report my failure. Funny thing is sometimes you just want to see if a reasonable proximity of a signal exists vs spot on accurate. I've also had some luck powering some (not all) switchers from isolated DC, depends on the APFC. I don't recommend that either.
Thanks,
Jeff