When Adcritic, which has similar growth to Youtube, went under the popular conclusion was that the cost of bandwidth was too high and that nowadays with cheaper bandwidth, this business model works. Adcritic had videos of ads - the argument was that they wouldnt get sued cos advertisers are happy if people watch ads. But they did - cos the middle men who arrange royalty payments to actors in ads felt threatened and put a spanner in the works. When an ad is being aired all the royalty payments are sorted, but if you show it months later then unless you can arrange a byzantine web of payments yourself (which is not viable for Youtube) you are as vulnerable as adcritic, no matter how cheap your 2005 bandwidth. Much of Youtube's content is user generated, but most of this is crap, the most viewed items are non user generated clips that Youtube does not have the rights for and some of these are memes like the matric ping pong clip that have been doing the rounds of the web for years. The answer to whether Youtube's impressive growth is sustainable, will depend not on whether they have volume, as they say, but whether the volume contains anything othr than a vacuum. That will depend on whether new memes and quality content are supplied by cellphone captured video. The jury is still out on that one.