I did this , whilst it didn't crash immediatly it did eventually.
What I did notice was that before the crash I opened a movie in VLC and it made Safari and my twitter app shut down whilst my other open apps were unnaffected.
I must admit that this is the first time I have regretted upgrading an OS [and I've been using macs for over 25 years!!]. Apple really dropped the ball with this one. I'm not too keen on this whole download the OS rather than a dvd or usb drive start up disc as you're subject to 2 variances rather than just the one. IMO this smacks too much of a Big Brother direction.
I've read the other threads and there seem to be a lot of people getting rolling grey screen of death crashes and needing hard restarts.... the reasons are not 100% clear but it feels it's something to do with Safari/Flash/Other video apps
To all intents and purposes I cannot use my mac properly and my work is quite affected as I need to use Safari a lot. I looked into downgrading back to Snow leopard but I don't have enough free external HD space to back-up my existing new files so this is a no goer.
This fix needs to sent out yesterday!!