My guess is that it bites a fair number of people without them even realizing it. I didn't figure it out for a while myself because I was using the button in Mobile Safari that sends the URL of the current page to the address of your choice to do clipping before Ken implemented it, so I "knew" that I could mail from iPod to OmniFocus without trouble and thus assumed the problem must be elsewhere. And as I usually was only doing Mail from the iPod to OmniFocus when I was away from my computer, there was a decent opportunity to forget that I'd sent the message by the time I returned. I think the only reason I discovered it was trying to answer a forum post! Just goes to prove my theory that a good way to learn all about OmniFocus is to try to figure out the answers to all the forum queries :)