iTunes HD movies: cost-effective blu ray alternative?

 I don't have a BD player, and chances are I probably won't get one, because I have no intention of starting yet another library of physical media.

To indulge myself in a little HD viewing, I've been looking at iTunes again with renewed interest, and I've found that compared to their overpriced albums, their films look a little more competitive.

For example, I quite fancy Nick Park's excellent Pirates! in HD for the kids (honest), and the iTunes price of £13.99 compares favourably with the blu-ray price in Amazon and Play.com, both of which are £15+.

I also see they're doing MIB 3 in HD for £13.99, again reasonably competitive compared to the blu-ray's £15+ pre-order price elsewhere. What's more it appears I could download it now in advance of the 'physical versions' being released on 05 November.

But compared to BD, what kind of picture quality can I expect from iTunes HD films? We all know that high resolution means diddly-squat if the video has been over-compressed, and unlike audio, purchase-quality previews seem conspicuous by their absence (unless I'm looking right past a really obvious big button).