Even with following the optimization tips the payload is far too large.
Some of this is due to the Microsoft Ajax scripts. With version asp.net 4.0 you are able to choose which scripts are needed, and only include those, so you don't need them all.
I hope that telerik will follow a similar approach, so that you don't have to include a load of code that you don't use. This would help a lot.
I really like the telerik controls, but not everyone that visits my sites have really fast internet connections. a large part of the world is still using modems, or have less than fast broadband.
Another great article that can help: http://www.codeproject.com/KB/aspnet/fastload.aspx