It looks like deploying ASP.NET AJAX sites won't be as easy as we thought. Beta 1 of the ASP.NET AJAX Extensions now installs in the Web server's Global Assembly Cache (GAC). You can't just copy the DLLs into the bin folder anymore. Apparently, this change is because some operations require Full Trust.
Yes, using the GAC makes patches and updates easier: You can replace only one copy per server rather than multiple copies of the DLL scattered in the bin folders of individual webs.
However, this is real downer for people using shared hosting. Understandably, ISPs don't want to install beta software on production machines. That means sites that want to feature ASP.NET AJAX right away - or have deployed the CTPs - have to wait until the release version. (Microsoft keeps release dates close to the vest, so who knows how long the delay will be.)
Even after the release, ISPs can be slow (or refuse!) to install new components. It's unfortunate that these wonderful client-side enhancements can get mired in server-side issues and delays.
BTW, I'm still angry that I had to abandon an interesting Visual Studio Tools for Office (VSTO) project because the software requires Full Trust in my public web site. For security reasons, ISPs limit individual webs on shared servers to Partial Trust.