Comment by ack_complete

That might have been the transition from Visual C++/Basic 4 to 6 (I skipped 5), but the cataclysmic one was the switch from Visual Studio 6 to Visual Studio .NET, when large portions of the IDE and build system were rewritten in .NET. Visual Studio .NET (2002) was much slower and much buggier than VS6. The native debugger was glacial at conditional breakpoints and debug output, the build system took an eternity to do a dependency check, its UI visibly redrew more slowly, etc. It was so bad that Microsoft had to create a special offer for the Visual Studio .NET (2003) upgrade for only ~$30.

This transition was not great for Visual Basic developers either since their language was transitioned from generating native code (VB6) to becoming dependent upon the .NET Framework (VB.NET), supported secondarily to C#.