I've always stuck to 'blend' for my templates, but have seen a few punters decide on 'interpolate' when rendering HDV to SD (because of the change in field order). Although I've never experienced any problems with that myself, I've been digging around for more info. (You know that silly thing, when you think someone else is doing something better than you, even if you're quite happy with what you're doing? )
Anyway, it seems that choosing interpolate throws away half of your resolution. Plus it's crap with any objects not moving slowly. So, really my question is; How many here are choosing to interpolate? And what problems with 'blend' caused you to change?