The new product is an extension of their existing Video search that crawls videos on other sites. As a nice side effect of this, Yahoo Video has content right now, even before they get a lot of videos uploaded to their system. Yahoo took a similar approach in Yahoo Local; restaurant reviews entered on Yahoo are supplemented by restaurant reviews crawled from the Web.
A big problem with Yahoo Video is that it does not convert all the videos to Flash. As Paul Boutin said:
The guys behind YouTube hit the sweet spot ... They made it head-slappingly easy to publish and play video clips by handling the tricky parts automatically.Simple enough that grandma can use it. That's the sweet spot.
YouTube's servers convert your vid to a standardized format, but you don't need to know what that format is. If you send the URL to your aunt, it'll play in her browser without spraying the screen with pop-ups and errors.
There's no software to install, no settings to muck with. The video auto-plays as soon as you load the page, without launching more windows.
See also Michael Arrington's review.