You can't really tell, because not all 3 minute videos will have the same file size. Some video formats may be larger in file size than others. Take .MPG files for example, they are usually larger than .WMV files. I make and upload videos to YouTube all the time, and I think a 3 minute video would probably on average be around 30-50 MB's in size.
Are you sure youtube doesn't compress them in anyway? because I'm sure I'm not downloading 50mbs every video I watch.
Depends on the quality of the video. Youtube changes all the videos into flv's anyway, so file format doesn't matter. But youtubes bandwidth must be through the roof...
Really? I would have guessed much less than that. Movies compressed to Divx are usually made to be about 700mb in size so they can fit on a CD. Most movies are about 100 minutes long, so that's 7mb/min. That would make 3 minutes of a Divx compressed movie about 21mb, which is right within your range. Youtube videos are not anywhere close to the quality of most Divx-compressed movies. I'm guessing Youtube compresses them much more, down to maybe 1-3mb per minute, so a 3 minute movie would be between 3 and 10mb.
I think it's much less than that. I'm pretty sure they cap the quality of movies as well as change it to an flv. I'd guess maybe 10-15Mb for a 3 min clip.