Sometimes one picture is better than a poem. In some cases, a short video presentation shows more than screenshots and overview. A good 60 seconds video can reveal product features and uniqueness or display it in action. Popular startups like Box.net or 99design.com embedded introduction video on the website home page instead of traditional features overview and images.
One the one hand, their idea to place a video makes sense for complicated products like file synchronization and design crowdsourcing. The plain features description and screenshots will not get you in the heart of the matter. The phenomena of synchronization and crowdsourcing are too hard to explain with words and charts. Thus, a little video presentation looks much more attractive explanatory tool.
On the other hand, a tiny video or not well-done video may spoil the whole product impression. Moreover, if the video loads too slowly, user may skip it or leave your site in search for a faster and better alternative. When you make an emphasis on the only home page video, you depend too much on tech aspects like the Internet connection speed, video player support, video format compatibility etc.
However, it looks a good idea to make a supplementary video which summarizes text overview or shows you a product in action. Thus, you can be sure that your site visitor will understand your message correctly whether by text description or by video presentation.