EDIT: I showed this issue to the Best Buy Mobile guy who had a Hero and sold me on my 3rd one when I came in to exchange the second one. He had shown me his and told me that he REALLY felt like I'd gotten two bad units, as coincidental as it might sound; he said his Hero was awesome and that he's never had an issue with his. When he tried to play back the same YouTube videos as me and he saw his handset FAIL, he had only two words: 1) Oh, and 2) Sh*t.
"See? I told you I'm not crazy. These phones are buggy as hell," I said to him. "Now I'm a little freaked out about my phone," he replied.
Good. He should be.
This is the difference between someone who USES his phone and another who doesn't use it nearly as much.
Damn glad I found this! I started having this issue - oddly enough - on my 3rd Hero inside of the 30-day return period (1st one got a lot of dust under the screen and then bricked, the 2nd one just acted up all over the place, and now this one won't play YouTube video 9 times out of 10).
I tried disabling Sense UI and a few other things to see if that was interfering, but nope. Also seems to be that it could be video-specific; some videos I can play over and over without issue, while others will never play, no matter how many times I try to play them.
I'm gonna send an email to HTC support citing the link to this page. I'm collecting a number of issues I've had with all three units along the way. It probably won't count for much (I don't think they care), but it'll make me feel better once I've accumulated a bunch of issues and fired it off to them.
I work for a technology/product company, so I understand that no product is perfect.
However, after 3 handsets, all of which have acted up, lagged, exhibited strangely sporadic behavior, and have simply failed to instill in me ANY confidence in their long-term reliability...well...I'm not pleased with HTC or their Hero. Not. At. All.
I dropped AT&T and my iPhone for Sprint and the Hero thinking I'd be saving money. I certainly am saving money, but now I understand more than ever the phrase, "You get what you pay for."