How can I upload HD video from iPhone 4 directly to web?
Regarding with how to use it, check out this post: http://islandinthenet.com/2010/07/06/pixelpipe-upload-720p-hd-video-from-iphone-4-to-youtube/ I recommend that post, it gives some great information on the app and how it is used.
Also, given this:
If you don't like the PixelPipe app, it shouldn't be too long before another solution pops up :)
According to this page, an app called SmugMug is also 720p uploading enabled, however I couldn't find much in reference to that on their site. http://www.tuaw.com/2010/07/01/want-to-upload-720p-from-iphone-4-try-pixelpipe/
There are many apps that do this. I like the following for ease of use and design. I'll rank them in the order of the quality of the final video (and coincidentally overall usability)
One last mention is a live streaming app called Ustream Live Broadcaster - I don't really use it but it's unlike the rest in that it's more of a broadcast tool than for pushing something you captured to the web once the video is complete.