VC++ Team Says:
Our first implementation of C++ IntelliSense appeared in Visual C++ 6.0 and we did this through the creation of a supporting file, the infamous .NCB, that contained consolidated references and definitions generated by the compiler. IntelliSense was pretty limited but still considered an outstanding feature as no other IDE at the time offered anything similar. The .NCB file contained a rich set of information including class members, global variables, etc. but we didn’t have complete information for such constructs as namespaces and exceptions. This deficiency and the fact that these files grew so large, complex and occasionally corrupted (who doesn’t remember fixing an IntelliSense problem by deleting the .NCB file and having it rebuild), that we needed to change the underlying implementation.
Great news for C++/CLI developers. VC++ Next will have Intellisense for C++/CLI. Read all about it here. It's great to see the VC team being so open about what went wrong in 2010 and what it took to make it right in the upcoming version.