it was the whole laptop which crashed, not safari. just mentioned i was using safari in case anyone said it was the software i'd installed which could be the cause.
not a massive issue as its very quick to boot on an ssd, but to have 3 years of non crashing vista (people are always slating vista as being rubbish) and the my 2 week old one to have done it twice is not what i expected.
That is very odd, when you say crashed, what exactly happened? Spinning beach ball? Completely froze? Kernel Panic (Very obvious, black screen telling to you reboot)?
An application that freezes can be "force quit" by hitting command+option+esc or by going to the apple menu, depending on how the application has frozen it may appear that you can't access the apple menu, in that case click away from the application to the finder and then you'll be able to access it.
I've not seen a "frozen mac" or a kernel panic for a long time, probably going back to Puma. If it continues to do it, I'd reinstall OS X and see if that fixes it.