Howcast, one of the leading video tutorial sites on the Internet, just released an iPhone application (iTunes link) that allows you to access their video content while on the go. Most of the videos on Howcasts have a very high production value and can teach you anything from how to cook eggnog to how to jump start your car. The app is very easy to use and allows you to search for videos, bookmark your favorites, or browse through the most popular content on the site.
One great feature of the Howcast web site that you lose when using the iPhone application is the great video player, which allows you to slow videos down, zoom in, or skip to different chapters in a tutorial. The iPhone obviously doesn't support Flash, so the Howcast app has to rely on the standard QuickTime iPhone video player.
If you don't know what you want to watch, the app will show a random video if you shake the phone, though this seems like more of a gimmick than a useful feature.
The iPhone application feels a bit limited when compared to the Howcast web site, but given that most of the tutorials on Howcast are shorter than five minutes and that the production values of the videos is very high, using the service while sitting on a train or bus might just give you a chance to learn how to forage for wild edible plants or how to clean your iPod earbuds.