I've run into this problem recently as well. Several days ago, the project was working fine with VS SP1 installed as well as the lastest AJAX release.  Then it suddenly started exhibiting behavior similar to what was described earlier in this thread.  In my case, somehow an assembly mapping for Analysis Services was added to my web.config and the project took an incredibly long time to load, most likely due to the Analysis Services assembly not being in my bin folder.

 So the suggestion from my experience would be to check your web.config for any assembly listings that aren't actually included in your project and then removing them.  This was the case for me.