I’m happy to report that in my short experience with Safari 4 (released as a public beta at time of writing), the tab sidebar at least seems to work beautifully still. ‘Top Sites’ tabs show a black thumbnail but everything else with regards to the tab sidebar seems to be in perfect working order.
Unfortunately, I have noticed that separator bookmarks (-:-) do not appear as menu item separators within the bookmark menu anymore. I have no doubt that this functionality will return soon in a future update.
If I enable the automatic Find function within SafariStand (under Safari 4 beta), Safari freezes as soon as I start typing when a page has loaded. Only a “Force Quit” will let me quit the program then. Too bad. Apart from that, I love Safari 4!
The auto Find function cause Safari 4 beta to freeze on my systems, as well. I got PithHelmet to work though!