I tried Safari 4 on my MacBook back in February when it first came out in beta.
It crashed immediately, every time, so I uninstalled it.
I upgraded to OS X 10.5.7 earlier in the week and new Safari bits were available,
so it seemed like a good time to retry it.
After all, it had been faster than any other browser on my Vista box at work.
Again, it crashed immediately.
This time, however, I took a closer look at the details of the
error report that was being sent to Apple.
A little Googling suggested that the Glims plugin was at fault.
Indeed it was.
I replaced beta 8 from September 2008 with the new beta 16,
and it's working again.
Glims adds search engines, thumbnails in search results, favicons in tabs, etc.,
so it's useful.
I haven't used Safari 4 much yet on the Mac,
but it seems like an improvement.