First time that I've tried to use "#" instead of "?" for url parameters was on the CPAN2Deb page. No page reloads needed everything handled by JavaScript. Yesterday I've tried that same, but for search.youonl.com. How does it work? Every time a new search is made the location bar is updated without a need for page reload. This is fast (the browser makes no unnecessary request to the web server) and it allows easy bookmarking or copy&pasting of the current search configuration.
Here are some examples:
The ";" vs "&" for separating the arguments is good because "&" needs to be escaped in HTML while ";" can be simply copy&pasted directly.
One side effect of switching from "?" to "#" for the url arguments is much more privacy for the clients as the requests with arguments are not passing to the server, so there will be no user queries in the server logs any more. search.youonl.com still uses Google Analytics for statistics, but the search queries are shared exclusively between the client (web browser) and the search engines that he uses.
And last, but note least, is that fewer requests to the web server means less processing and data transfers.