ASP.NET AJAX 1.0 has been released but you knew that. ASP.NET AJAX Control Toolkit has been released but you knew that, too.
What you may not have known is that the RoundedCornersExtender in the new release now features the ability to specify which corners you wish to round. The code looks absolutely nothing like my version and from my brief comparison of their code to mine, that's a good thing.
A nice little bonus: not only can you rounded specific corners (e.g. TopLeft, BottomRight) but there are shortcuts to round pairs of corners (e.g. Top will round both the top left and top right corners).
So I'll take my version of the RoundedCorners down soon but in the meantime, if you've hit this page from a search engine, skip it and download the real thing.