I'm not a dev. I've had iOS 5 beta 2 on my iphone 4 for about 10 days now, jailbroken with Redsn0w 0.9.8 beta1. Just a few cydia tweaks installed: Tetherme, iIfle, Open SSH, UISettings, 3G unrestrictor, Omnistat. Plus, I changed a few UIsound files, like email and sms.
I think it runs great. No crashes at all, except when I installed something I was pretty sure wasn't going to work (e.g., weathericon). Even then I just ran cydia from safemode and uninstalled the offending package. The only time I've even had to reboot tethered (other then when I installed mobilesubstrate) was when I accidentally forgot to put the phone on the charger overnight and the battery ran completely down.
I'm not encouraging anyone to install the betas. They're for devs only, and installing them without having access to a dev account is pirating apple software. Plus, unless you know what you're doing, you're likely going to have to restore back to 4.3.3 at some point.