just got a nec 3520 burner, yet to be installed. i haven't checked the prices of dvd-9 (dual layer) media yet, but the link above is the place to go for any dvd burning question.
I just don't think enough people have them yet for it to be profitable to sell these like the single layered yet. I bought the Sony DRU-710 about 5 months ago and still haven't been able to shell out the money for the dual layered disks yet. I don't even know what I would put on them. I don't know if the software I use burns dual layer movies or what since I haven't ever bought one to try it.