Expression Web Designer (EWD) is supposed to be a designer's tool for designing asp.net 2.0 applications. It has other roles but working on asp.net 2.0 applications is what interests me currently. So I tried running EWD on a real asp.net 2.0 project. EWD looks nice, seems nice but I immediately stumbled upon a serious limitation.
EWD won't show 3rd party controls at design time nor it will provide intellisense help for them. At first I thought I was missing something. But no - support for 3rd party controls is really missing. Imagine Visual Studio without showing 3rd party controls at design time. It would cripple its designer very much and the same is true for EWD. Seems like [MS] forgot to eat its own dogfood on this and they also never used EWD on a real asp.net 2.0 project, not just a demo that uses out of the box controls. Or it was a deadline that forced them not to provide this support. Whatever the reason is it makes EWD much less usable on asp.net 2.0 projects.
There is a partial workaround though. Seems like installing 3rd party controls in GAC helps with intellisense support.
If you consider this feature important, then do vote for it at [MS] Connect: