I know it depends on the bitrate of the video, but in general if I want to watch youtube, hulu or netflix without constant interruptions
is 1.5 Mbps good enough? is 3.0 Mbps good enough?
Well video can be streamed on any type of connection, it's all a matter of how well.
In a perfect world scenario a 3Mbit connection would work well. The problem is that you will probably not get 3Mbit consistently.
I would recommend at least a 6Mbit connection for a smooth video playback and a 10Mbit connection for seamless playback.
I have a 10Mbit connection and I get max quality on Netflix via my Xbox360 most always.
I would generally agree that 5 to 10 mBit would be required, but there are several factors that determine this. First is size, a 640 by 480 VGA is much less data then a 1024 by 780 video. You can get decent video at low bandwidth with small sized videos, like 320 by 200. Next is compression. Almost all videos are compressed to reduce the amount of data. Some compressions are better then others, but the most aggressive compressions are lossy compressions, you lose information. Third is consistency. The available bandwidth often fluctuates dramatically. Most video players will buffer the data to prevent this from showing up during the playing of the video.
1.5Mbps would probably be enough for Hulu. I have 1.0Mbps and it has a short hiccup every 5-10 seconds, so I'm just short of having enough for Hulu... :-(