I don't use VS 2008 yet, so I can only speak for VS 2005.
It doesn't support C99. Support for C89/90 has always been good in VC and I'm not aware of any non-compliance issues with it.
C++98 support has a number of issues, some of them are documented by MS as known issues and some are plain bugs. I made a blog entry to use as a "notebook" for various VS 2005 C++ bugs I encounter in practice. If you wish, you can take a look here, although this list is probably far from being complete
