Q: OSX Lion + 2011 iMac 27'' + Video = Freeze

By the way Justin.tv is the only site giving me that behavior. I would really like to know if its just me.

@nFocus

Thank you so much for sharing! It fixed my problems and now I was able to play a lot of Youtube videos again without a single issue. Usually it started with video 'artifacts' in the Dock / top menu when I opened something video related (Youtube, Flash banners on websites or MP4 in VLC) and the iMac crashed a few seconds later.

I personnaly can't replicate the issue on an iMac Mid 2011 running a clean install of 10.7.

Adding another voice to confirm that I have the same issue on a brand new fully specced 27" 2011 iMac.  I've experienced GUI artifacting and jittering of Flash-based video (YouTube and other sites), and Quicktime videos, followed by the system freezing where only the mouse pointer was responsive.  Force quit was not an option since neither the keyboard or dock were functional. A hard reset was the only way to recover.

I've now rebooted with the PRAM reset, hoping that will at least temporarily work around the issue until a proper software/firmware fix is released. 

Not sure if you were able to reproduce the problem before but after the PRAM reset, I think most would be interested to see if you get the problem again.

I reset my PRAM yesterday, and this morning, i had the bug on a youtube video :/

I can confirm this too. I've reset my PRAM twice and the bug still exists. Everyone but TUAW is quiet on this issue and nothing yet from Apple. VERY disappointed in the way Apple is handling this.

Open up Network Monitor, and you should see what's hanging and what's sucking up memory...

I found after I did that... my system probably needs memory, as when I get low on memory it locks up, this however has never been the case in Snow Leopard.

I have 16GB of ram. I don't think thats the cause. My money is on a driver issue.

I've got 12 GB.

This said, how many people have more than just the basic 4 GB, and how many have third-party RAM, as opposed to additional RAM purchased from Apple? (Mine is third-party.)

Mine is also third-party. But as I said earlyer in the thread accorind to memtest everything is fine.

This is not a memory issue, it will do it from a cold boot after sleep with no other apps running.

mine did that about 10% of the time when I first installed... I removed all boot up apps and removed my Applejack and the issue stopped.

12gb of ram in mine 8gb non apple.  Dont think this a memory problem, Ive been running snow leopard without any issues it only seemed to be after the Lion upgrade and clean install that this issue raised its head. Tried reseting the PRAM here also, but still no joy.

Seriously thinking of going back to Snow Leopard as no stability issues with it.

I'm pretty certain it's not RAM. But since I was called by an Apple technician earlier today, we've been exchanging emails as he's asked my to try certain things (deleting caches, trying to view videos in different ways, etc.). One question he asked was about RAM. It's unlikely, though, because, as you say, there were no issues with Snow, and the first 4 GB isn't even used when I restart and view a video right away, so the third-party RAM doesn't get hit. (Some years ago, with a Mac Pro, I had a problem like that; only when the 4th RAM card got used, would I have problems. Took a while to figure it out.)