One aspect of the whole Dual Layer situation has not been mentioned in this thread, which is that this is
only DVD+R Dual Layer. DVD-R Dual Layer won't appear until early 2005 (according to pundits).
Note that according to a
test of 1,000 different players and drives, DVD-R has significantly better compatibility than DVD+R:
Compatibility results: DVD-R=96.74% DVD+R=87.32%
What this means - especially since, at this point, only a handful of people have burned a Dual Layer DVD - the added DVD+R Dual Layer capability may be less than useful, especially since it uses a format with less than perfect compatibility.
I myself was drawn to this thread, because I'd like to get a DVD burner that isn't missing some capability that will be useful in the future, but the more I research this, the less I think this particular capability is that sort of feature that makes a difference.
For example, most DVD movies now come in a case with 2 DVDs, one for the film, and the other for the special features. The fact that there are two disks instead of one is really no big inconvenience. Similarly, burning to two DVD5's, instead of one DVD9, is not going to be such a big difference - especially considering that it is going to be
way cheaper to do so for at least a couple of years, if not more.
I think we are still 6 months from the "future proof" DVD burner that does both DVD-R DL as well as DVD+9 DL, so it might be better to save the $20 for a future upgrade.
[later]
After reading a bunch of messages in several forums, I think that the NEC and Pioneer burners are probably the best two units, and that the NEC 2500A is approximately equivalent to the Pioneer 107D, simply due to the fact that not one can make a convincing claim that one is better than the other. So, the 2500A is better simply by being about $20 less. And, for the reasons above, the 2510A is not worth $20 more either.
So, I ordered an NEC 2500A for $68.99 shipped from NewEgg. The bonus is that you can download an unofficial, warranty-voiding firmware upgrade that will add Dual Layer capability to it, which I will download and save for the probably unlikely day that I end up wanting to burn a Dual Layer DVD at 2.4x for a similar cost to a pre-recorded DVD movie. Just having that file is just as good "future proofing" as buying the 2510A with the lens factory-adjusted for DL, since DL will be impractical for a long time to come.