Last week my corporate network administrator pushed out a couple of windows updates for SQL Server 2008 R2 and Visual Studio 2010. After installing them I discovered that my intellisense in SQL Server management studio had disappeared. No matter what I tried, I couldn't re-enable it.
The intellitrace in VS2010 SP1 causes an issue with the intellisense in SSMS 2008 R2 and Microsoft are aware of the problem and have issued a hotfix. Scott Guthrie blogged about the issue but doesn't mention the fix, and Microsoft don't make it easy to get your hands on it either.
The SQL Server 2008R2 SP1 is supposed to contain the fix, but I found that the issue was still there after installing SP1. After chasing my tail for a while, I found the easiest fix was simply to restore my system back to before the updates were installed.
For Windows 7 go to Control Panel --> Action Centre and select 'Restore your computer to an earlier time'.