(As an aside, I'll use the term ‘mobile’ in place of ‘iPhone and iPod touch’. Seems reasonable.)
The built-in YouTube application on my iPod touch seems inexplicably slow. Sure, it's loading the videos over WiFi, but so is my MacBook Pro. And decreasing the distance to the base station doesn't help—it's dog-slow if I sit the iPod on top of the Time Machine. Videos seem to load over several multiples of their duration. A two minute video takes five minutes or more to fully download. What's the issue here? Encoding formats and a slower processor on the mobile device? (That is, is it decoding on-the-fly during download, and is the decoding incredibly CPU-intensive?) I just don't think WiFi is the rate-limiting step here.