It took me a while to figure this out because its problems weren't immediately obvious. There wasn't a flood of howls on the Mac blogs, but it seems to be rather buggy in many subtle ways. Pages that used to stay logged in if I left them open in the Dock now close themselves. The Rainbow Wheel of Death is a more frequent visitor regardless of how often I empty cache or choose the Reset Safari command. 1Password does not work as well when used to log in to password-requiring sites. Normal sites seem to work properly, but sometimes the wrong page loads when I open a bunch at the same time using Open in Tabs.
As a result I am recommending that you stay at version 5.0.5 if you are there now. If you are at 5.1 or 5.1.1 and don't seem to be having trouble, stay there. Sadly, it's next to impossible to downgrade Safari to an older version because there are so many pieces of itself scattered all over your Library folders.
Tiger 10.4.11 users are not included here because the final version of Safari for you is 4.1.3. If you need to do banking or commerce, find the latest version of Firefox or Camino that will work for you. In FF, I believe that's version 5; Google Chrome does not have a Tiger version. Otherwise forget about using the more security-oriented sites.
No serious problems have come to light with the other updates issued by Software Update. Go ahead and get the ones listed, but you can highlight and delete ones for programs you don't have or use, such as the abandoned iWeb, or any of the iWork suite of apps that you did not actually buy. Those sitting on your drive are demos and can be deleted to free up space. Also feel free to get all MS Office updates and Adobe updates, avoiding upgrades to Reader beyond version 8 which offer you no advantages and strip out an important feature.