Search has a new look. I'll be honest. I really don't like the new Safari search look. The screen dims and keywords highlight. I find the dim display hard to read and I keep wanting to adjust my screen brightness. I wish there were a way to search using the new highlights without the dimming feature.
Text Fields resize. The diagonally-striped resize handle now appears in the corner of text fields, allowing you to resize them as needed. The resizing happens live on the Safari page and the rest of the web page adjusts to accommodate the new size. It's a nice touch--albeit one that I'm not sure I'll use much.
You can drag tabs. Safari now allows you to reorder your tabs by simply dragging them to a new spot. I'm not entirely sure how I'll use this, but again it's a nice feature to have.
Tab closing warning. I don't remember seeing this before outside of Firefox: Safari will warn you when you attempt to close several tabs at once by clicking the window close button. Forgive me if its not new to Safari 3, it was new to me.
Google server search. If Safari cannot find a server when you enter a URL, it now offers a Google search box on the error page.
You can drag tabs out as new windows. Safari 3 lets you grab a tab and drag it out of the tab bar or onto the desktop where it morphs into a new window.
Spellcheck is improved. Safari's built-in OS X spell check features seem to be working a lot better and more consistently than they used to.
Add bookmarks for N tabs. A nice new bookmarking feature that lets you add more than one new bookmark at a time based on the number of open tabs in the currently displayed Safari window.