Briefly parused Tom's DVD-drive roundup, and reading the conclusion, one thing they pointed out was that they were unable to find any DVD-R DL media. But with DL discs costing 3-4 times as much as a regular DVD, it's hard for me to justify using them for anything (even though I own a DL drive myself).
DVD-R is only slightly more compatible w/ standalone DVD players. Any standalone made today will work with both. Any standalone player made in the past 3 years will work with both. I have one of Sony's first DVD standalone players in my kid's room and it reads both just fine.
Not many generic burners out there do DVD-R DL. Mostly cause DVD-R sucks IMO. DVD+R has always been the prefered format by most. However, tomshardware recently did a double layer roundup and the name brands support DVD-R DL up to 8x (NEC, Pioneer, Toshiba, and Sony).
As for the DVD-R DL media... apparently Tomshardware and others aren't looking hard enough. Here's a list of websites with that media:
I'm with HD-DVD on this one. The problem with Blue-Ray is that it is being pushed mostly by content creators (i.e. Whatever Sony's movie studio is). As such, it's looking to be more restrictive on fair use options and copyright protections. Conversely, with Microsoft and Intel now backing HD-DVD, and their push for the next year being heavily focused on media centers (VIV and XP Media Center Edition), they're helping to make sure that some consumer rights are thrown into the mix.