I've noticed some improvements:
1. I have a few auto-click bookmark folder with my favorites, between 10 and 14 sites that will open simultaneously upon a single click to the Bookmarks Bar. Before, they would (a) take a long time to load, and (b) as long as any one of them was loading, any page viewed would get the spinning beachball until the last page finished loading. After the update, the pages now load noticably faster, and once a certain page is finished, it is possible to scroll up and down and click on a link without the spinning beachball, even though one or more other pages in tabs are loading. In such a case, performance is slower, but the beachball no longer stops you dead.
2. In a similar situation as (1) above, when I had many tabs open, some of them would auto-update every x number of minutes, like Google News. When that happened, even if I was using a different window, I would again be beachballed. Now that interference is substantially reduced, though it does still happen some.
3. On some sites, especially ones like the New York Times, any attempt to select text, especially multiple-clicks on text, would result in wait times of up to 5 seconds per click--for example, if I double-clicked a word, I would have to wait for about ten seconds before the screen unfroze. No spinning beachball, but I simply couldn't do anything--scroll, switch tabs, etc. With the new version, that wait time on the same sites has been reduced to less than a second per click. Again, it still happens, but much faster.
***
A bug that still exists, aside from the ones listed above, is the first-window-popup-after-unhide bug. If you open more than one window in Safari, and are looking at a window other than the first when you hide the app, then unhide it, the first window pops up--even though any action you attempt will affect the window you were looking at when you hid Safari, despite that window being hidden behind the first window.
***
So, as I see it, there are some fixes, but some annoying bugs still persist. I was almost ready to switch back to Mozilla/Firefox when this update came in. I'll probably stay with Safari now, but not for certain--I'll have to see how it performs in the long run, if the fixes degrade over time, or if the 'fixes' I noted are not fixes but rather simply performace bumps due to the freshness of the version. I'm still annoyed by the bugs, but this version seems more bearable, while allowing me to enjoy the features Safari offers.