I've ran in to this in two completely different environments now. I can build the solution and not have any problems with intellisense. If I deploy our Web Parts project to my local SharePoint 2010 site, as soon as the deployment process hits 'Deploy Succeeded', intellisense blows up, and I get compile errors on the current page. I can go and select each project in the solution, click refresh, and everything is good again.
Any ideas? Can anyone explain this?