Maybe my eyes suck (I do wear contacts), I don't know. But to me, Blu Ray looks no better than DVD on my HDTV. So, when buying movies, I'd probably go for the Blu Ray or combo pack, but mostly because of the extra bonus features.
The only time I've seen a difference was on people and store displays that have the "soap opera effect" going on, which looks like crap. Seriously, why was that invented?