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.