Several readers have commented (eg, here and here) that they're having trouble posting to YouTube Mobile, despite my having written that it was working for me (here's the video from then) so I'm testing it.
At 12:50 (local time) I sent a short video clip (around a quarter meg) from my TyTN to my YouTube Mobile address, via e-mail through my USB connection.
Note that I'm not testing MMS or e-mail over 3g or Wi-Fi at this time. I think that YouTube Mobile should be the same for all e-mail routes.
At 12:55 I see that the e-mail has arrived in my Yahoo e-mail account (I BCC'ed myself).
At 1:20 it still hasn't arrived on YouTube in My Uploaded Videos.
So something does seem to be wrong. Last time I saw the video as an entry in My Uploaded Videos very quickly, with a note that the video was being processed. But now there's nothing there.
I'll update this later if it shows up.
QUICK UPDATE A DAY LATER: The video still hasn't shown up on YouTube, so it's definitely not still in transit. I tried sending the same video from another e-mail account, and it didn't show on YouTube, so the problem isn't with the TyTN or mobile connectivity.