Thanks to Apple's official extension API introduced in Safari 5, there are now several native and free extensions that alleviate, if not entirely eliminate, these Safari shortcomings. The one I wrote is called PopSearch. It makes adding arbitrary search engines to Safari pretty easy; and using them, fast and convenient.
Now, you have to understand that native Safari extensions are not allowed to modify the address bar or the search bar, so PopSearch will still not let you search from the address bar. Instead, it does what seemed to me to be the next best thing: when you press a customizable hotkey (Command+K by default), a small search bar pops up, where you can enter some search terms, select an engine, and press Enter to execute the search.
PopSearch has a few nice features:
- To better approximate the address bar search feature of Firefox and Chrome, you can select a search engine by typing a short keyword before your search terms.
- To open the search results in a new tab, you can press Command+Enter. To open them in a background tab, press Command+Shift+Enter. You can configure PopSearch to use a new tab or background tab by default, in which case these modifier keys have the opposite effect.
- If you select some text on the page before invoking PopSearch, that text will be automatically entered into the search input field.
- PopSearch will optionally remember your most recent search queries, so you can repeat them without typing.
- Site-specific searches are supported using Google and Bing. This means you can quickly search just the site you are currently on.
- You can add new search engines to PopSearch manually (by entering a search URL), or more easily by using the 'engine wizard,' which will try to detect the correct search URL after you execute a search the normal way.
- You can customize the appearance of the search bar using CSS.
[crarko adds: I tested this, and it works as described. This author submitted a few of his Safari extensions for consideration as hints, and I thought this one was a good representative example. There were some other interesting things and I refer you to his web site to take a look at and try them out if you like.]

