Since it all began in VC++ 6, IntelliSense has been improving in significant steps. However, there's always time when it stops working. Whether sooner or later depends on how the code is written and how big the project is.
In the current version, IntelliSense hates changes happening inside class declarations in header files... It simply makes it stops working in most cases, and you'll have to close the solution/reopen it again to get it back working.

I know it's not a trivial task at all (even that other 3rd party plug-in fails sometime!). Any information on when should we expect a version of IntelliSense that REALLY works under big projects' pressure?

Wessam Bahnassi
Microsoft DirectX MVP,
Electronic Arts Montreal