Last week at SES, Yahoo! added support for dynamic URL rewriting. Basically, this is a new feature in Yahoo! Site Explorer, that allows you to specify parameters on your URLs that you would like the Yahoo! crawler to ignore. After years of helping people get rid of Session IDs on their URLs, this is a really great thing to see. You can read the details on Dynamic URL Rewriting by Yahoo! here.
Yahoo! has continued to push on these types of features, and so has Google. I would like to urge the search engines to collaborate on these features. Ultimately, it's the availability in all the search engines that makes them powerful. As it stands now, if I had a client with a dynamic URL parameter problem, I would have them setup the new feature in Yahoo! as a stop gap, and still be working with them to get them removed because this feature is not supported by Google.
Props to Yahoo! for adding the feature, but now I need it from Google too. There are plenty of areas in which to compete, most notably that of search quality, or in new frontier areas of search. In the area of making the webmasters job easier, I believe that all the engines will derive the most benefit by collaboration.