You know what would be a cool feature (and even a useful one) to Gmail?
I haven’t received a video as an attachment on my Gmail for quite some time now, but I see no reason why it shouldn’t work same way as it works with previewing attached images.
Gmail could convert the video on the fly to a Google Video/YouTube private film, one that is not posted on the site and is only available to the people using Gmail and allow me to preview it directly.
It’s funny that Gmail gives ~3Gb of space to save stuff but I’m then stuck on downloading 5Mb of some stupid movie someone sent me just to view it, instead of getting a buffered near-real-time viewing experience, the same way I get with pictures (though pictures of a rather built-in support inside browsers, which makes the previewing if images very easy to implement and use).
It will also save some bandwidth to Gmail due to the fact that the encoded stream that goes through the Flash player of Google Video or YouTube is in a lesser quality than the original movie, thus allowing most people to view it in a lesser quality (which should suffice to most people) and not download the whole 5Mb+ file.
Gmail team, what say you? (or am I already suggesting a feature that is in the works…)