ENTERPRISE S1 set arrived yesterday, and I'm slowly picking my through it. One thing I noticed straight away, which won't make any difference to anyone in the US, but makes this worth reowning, is the different sounding audio. Because our SD TV system is PAL, everything film-based is sped up slightly. I doubt many in the UK even notice. More and more do, as they watch films on a format capable of 24 frames per second.
Even "Faith of the Heart" sounds a bit more tolerable now it's deeper!
This was the first thing I noticed when I watched the TNG Blu-ray sampler disc last year. It was the first time I've ever heard any Star Trek show at the correct pitch. An unbelievable difference; I can't imagine how anyone wouldn't notice.
I have literally every single series on DVD, all PAL. That means I'll have to upgrade to Blu-ray all at once - no way can I stand changing pitch mid-series. Madness!
EDIT: It also means all our episodes are slightly shorter. We've been getting ripped off for years!