Files folders places is looking for file names as you type under your ~/ (or absolute file if you start typing an absolute filename). The matching is done in exact matches.
If you have a file named /home/user/foobar.txt and type 'foobar.txt' you are offered to open the file.
It also look for gtk bookmarks (visible in nautilus or the filechooser) which you can invoke by typing their name.
If you have a bookmark called 'Work' associated to /home/user/files/Work, type Work and it offers to open the directory.

Search for files just launch gnome-search-tool with the given query and start the search in ~/

I hope it's useful !

So deskbar doesn't actually do any searching of its own, just links to lots of search engines? This is important for the introduction section text.

Regarding launching gnome-search-tool -- this is now quite out of date compared with nautilus search. 

Yes deskbar does't really do any searching, except in some special cases where no other solution exist.

About nautilus, i know but i need time to look at the nautilus command line api to see if it can be integrated..

Ok.
But now I don't understand what deskbar is meant to be.
Your webpage says:
'The goal of DeskbarApplet is to provide an omnipresent versatile search interface. By typing search terms into the deskbar entry in your panel you are presented with the search results as you type.'

-- but it doesn't give me any search results.
So I don't know how to write the manual for this as I don't get it.

I see :)

Let me explain.
Deskbar in itself is just an entry that sits in your panel (or a button if you choose so). You can write things in the entry and those things gets passed to a number of so-called handlers or plugins or extensions.

Each one of these handlers receive the user-entered string and do something with it. For example:
* the file handler will try to check if the string matches a relative or absolute filename on your disk. If so, it will offer to open that file or directory in nautilus
* the beagle handler will pass the string verbatim to beagle search and display the beagle results. Each result will be in the form of an action depending on the type of item returned by beagle. It could be a file (open file) or a conversation log (view log) or a browser bookmark, etc
* the evolution handler will pass the string to evolution contact book and evolution will match the string against a selection of attributes such as name, email, phone, etc. The result will be in the form of an action 'Send email to xxx'
* The history handler will match the string against previously used strings so that if you retype the same thing twice the previously used action will re-appear on top of the list so it's easier to access, generally with two or three letters.
* The browser handlers (search, bookmarks, history) will match the string against (smart bookmarks/search engines, bookmakrs, title of website in the browsing history) of your favorite browser. It will then allow to open the webpage or perform the web search as actions in the list.

I can continue to describe every handler if you prefer or if you have any doubts. I just hope this clarifies the situation a bit ? Otherwise you can always ask me questions..

I gather the gist of how Deskbar works, thank you.
I guess what I mean is that I don't see how it's useful.

I don't have the Beagle plugin available -- that would actually make it more like what I'd expect -- some actual search results instead of just links to things that might give me results.
I see the Google plugin, but it says something I don't understand about a file needed.
I've just enabled the Yahoo plugin and that seems to give me results.
But many of the plugins seem pointless to me. Eg, I just don't get the purpose of a link like 'Look foo up in Dictionary'. If I wanted to do that, I'd run the dictionary. Why doesn't it give me the results instead of second-hand links?

deskbar-applet development has been stalled [1]. Maintainers don't have future development plan so i am closing the bugs as WONTFIX.

[1] http://mail.gnome.org/archives/desktop-devel-list/2011-June/msg00073.html