As the owner of a blu-ray player, I'll tell you the one thing that makes me reconsider every time I think abut dropping $20 on a Blu-ray: compatibility.
If I buy a new Blu-ray, I can watch it in high-definition, but it must be on my living room TV. However, if I want to watch it in my bedroom, at my girlfriend's place, at my parents' house, or at the houses of any friends or relatives, I have to rent or buy the DVD. And that DVD will at least be upscaled in my living room.
The one thing that would make me buy more Blu-rays is including a DVD version in the same package. None of this "Digital Copy", DRM-riddled crap. It's not hard to do - they make standard double Blu-ray cases. I think just a week ago I saw a commercial for some Disney movie where they finally did that, and they should keep it up.