In case you are one of the hapless souls who, like Triskaidekaphobia, installed the Safari 4 Public Beta for Mac and have a humongous collection of bookmarks in your bookmark menu, this tip may save your sanity.
When switching to the bookmarks menu, Safari would beachball to the point of uselessness. Even moving the scoll bar up or down one bookmark would bring back this behavior. Although the Cover Flow functionality was completely hidden, we still suspected it was the culprit. We were right.
Using the collection of additional Safari 4 Beta hidden settings hint at Mac OS X Hints, we disabled it by typing the following in the Terminal (without the line break):
defaults write com.apple.safari DebugSafari4IncludeFlowViewInBookmarksView -bool FALSE
Worked like a charm, and bookmarks are usable again. This is useful for those who, you know, actually want to get work done n’ stuff.