the announcement, it only works in the US and UK -- but to make it work, after visiting the WP7 Visual Search, I had to change my location (in the top right corner) to "United States - English." Then I had to visit the Visual Search page again. Presumably this will also work if you live elsewhere, too.
The Visual Search itself is beautiful. The app icons slip and slide around the screen, and panels fade in and out with consummate smoothness -- it's powered by Silverlight, of course. Unsurprisingly, it looks and feels a lot like Zune -- and indeed, you can click through from any app to the Zune. From there you can install apps onto your phone.
The thing is, this tool in itself is nothing special -- but look at the competition! Apple's Web presence is alright, but it's hardly a joy to navigate -- it simply functions as a "preview" for those without iTunes. Google... well, take a look at the Web-based Android Market and decide for yourself. Microsoft's WP7 visual search seems positively awesome by comparison.