[Yoshi63]

I found them very useful when learning resteal stacksizes, final table strategies, ect... Since then, I have found them most useful in settling my play down if/when I go on a semi-prolonged tilt. I think they can be good for spotting leaks in your game, but you'll probably need to do additional homework to fix them.

As for specific videos, most people find JBax's pretty helpful (plus he makes it entertaining). Besides that, I would check out BelowAbove's videos, and apestyles' million video. Also, Rizen (despite being a more cash game player) has put out some MTT's with excellent commentary.

Edit: Oh, and make sure to at least check out some of the "live recorded" videos. Rizen did a 4-part one titled "MTT-R: Live Play". Live videos have a different feel than the hand-replayer ones, and you'd be missing a lot if you stipped them entirely.