1. YouTube was constructed with a community in mind.
Its interface tools, such as tagging, a rating system, comments, friends, favorites, friends' favorites, etc. go far beyond what Google Video provides for letting the community of users connect.

2. YouTube's user interface is vastly better.
It's easy to use and more attractive while ironically retaining a Google-like simplicity. Google Video's UI is so spartan as to be unattractive.

3. YouTube's viral functions -- "Share this video" and "tell a friend" -- are ridiculously easy.
The functions are automatically added at the end of each video, making each video simple to share. The brilliant seed of YouTube's model includes code for each user to play YouTube's videos directly from their own blog or website. Google's viral functions are found in the user panel under somewhat obtuse links called "put on site" and "send link."

4. YouTube videos always load and play faster than Google videos.
At least that's been my experience on two different computers in multiple locations.

5. YouTube displays the number of times each video has been played.
That's a data point of pride for uploaders. Google Video most likely compiles that data but does not display it. Data transparency is helpful for both content creators and viewers.

6. YouTube's user account system is more robust.
It's also easier to use and filled with more data than Google's.

7. YouTube's search functionality is vastly better than Google's.
That's a surprising outcome from the world's search leader. YouTube can sort search returns by date added, title, view count and rating. Google Video's search sort is by date and title.

8. YouTube displays three random images from each video for search returns.
That makes it considerably easier for users to find specific video files from large batches of results. Google Video just displays the first frame of each video file.

9. YouTube displays trackbacks to each video.
Google Video does not. YouTube's functionality there makes it easier to discover who the more influential virus-spreaders are.

10. YouTube helps users find the obvious: related videos.
It's a great tool for users trying to build video evidence related to a subject. For instance, go to the comments of this video to see the "related video" functionality