As part of my effort to port to VS2005, I updated to the latest version of STLport, 5.1.0. I've now reconsidered this and have switched to the STL built into VS2005. Here's why.
Years ago, when I initially switched from MFC collection classes to STL, I ran into one big problem - STL didn't have any debugging code to check iterators or array bounds. This caused random mysterious failures in the field in my first product that used STL when I didn't understand that certain operations invalidated iterators. I spent months working the problems out of that product. As part of that effort, I switched to STLport, which was much more robust than the STL implementation in Visual C++ 6.0 and STLport had debugging code in it to trap invalidated iterators, invalid array bounds, and other such programming errors.
The version of STL that ships with VS2005 benefits from Microsoft's security push and has had code added to check for problems like invalid array bounds. The VS2005 STL also has extensive debugging code that goes away in the release build. So my original need for STLport has ended. Even so, since my code was already thoroughly tested with STLport, I thought it best not to switch.
Today I was enduring my normal frustrations trying to debug an STLport set, which is effectively impossible to view in the debugger. I had the same problem with STL collection classes in VC6. Then I discovered that the VS2005 debugger actually understands the version of STL that ships with VS2005 and will automatically display the elements in collection classes such as set and vector. This is a huge timesaver and was enough justification for me to drop STLport.
Update 12/18/2007: A set of debugger visualizers has been published for STLport. Go to this link.