We don't even have 4x Blu-ray burners yet, but that didn't stop TDK from showing off
6x speed recordable media recently in Japan at the 8th Data Storage Expo. They also showed off a quad-layer 100GB Blu-ray disc, although it was only a prototype, they do expect to ship 4x discs before the end of this year. We're looking forward to burning 25-50GB at a time, we're not looking forward to waiting an hour for it to finish. These high speed discs need to get here and fast, HD DVD-Rs need to get their speed up to compete (actually, they need to become available at all but thats just splitting hairs).

http://www.hdbeat.com/2006/06/29/tdk-shows-off-6x-bd-r-discs/