It seems to continually crash Safari, for me at least. If I browse in a single tab, it's ok. But if I have multiple tabs open, like now, I can be reading something in one tab ( news for example) then switch tabs to U2start and the browser will close. When I reopen Safari, it loads up a previous 'stable' session with my tabs from a few minutes ago.
It was doing that to me a few months ago - it'd just black out and then throw me back to the springboard. Then for some reason it stopped and started running perfectly again.
No idea what the cause was; which OS version are you running?