On the main website, you can access directly some shows and channels. On the G1, it's quite limited. And not all the video available for the regular browser is available for mobile viewing. And the search function is abysmal.
The other day, I ran across an old Sherlock Holmes movie. I was able to begin watching it on my Macbook but I also had to leave for an appointment. I tried searching for it on the G1 but I wasn't able to find it directly.
Then, I resorted to e-mail the Youtube link to myself.
Once I received the mail on my G1, I clicked on the link and picked to watch the video through the Youtube app. And to my delight and relief, it worked!
I don't know why some video work and others don't. I just tried an episode of Fullmetal Alchemist and Robotech: The Shadow Chronicles. Both worked but MacGyver didn't.
I don't know why that is. Maybe one of our readers can shed some light on that. Until then, it'll be hit-and-miss. This way, you'll get more hits.