word of advice, I have mentioned in another post.
If you make something that is already exist -- Youtube...then you need to build something better than them, it is no point of providing a service that someone already had.

Example:
Friendster - been popular once because it links up with friends and friends. Blog system in which other friends will get updated.
Facebook - API, allow 3rd party to develop application onto them and linking across Facebook and Myspace. A hell out of a lot of features upcoming which beat Friendster in just one night.