See many small video sites all over the place. These YouTube-type sites allow you to add yr own videos or download them. Since there are already big general ones like YouTube , DailyMotion, is the demand/ market for such sites? Or may be there is market for niche video sites (like dance videos or music videos or comedy videos )but not general (anything and everything)?
In my opinion all those vertical niche that you mentioned music, dance and comedy comes into entertainment category which has wider scope all together, you can find tagging for specific niche in video sharing sites, youtube would be best if you're trying to promote those videos since youtube continue to its phenomenal growth.