I started Win32 programming with WTL. No MFC experience at all.
For those of you who may be curious about this technology, here are a couple of points:
WTL is a collection of header files with the source inlined in. Personally I find the source reasonably understandable. I have had not much trouble stepping through and debugging WTL calls.
It's a light wrapper around the Win32 API. Some people commented on the lack of documentation regarding the WTL. The truth is, MSDN's API and common controls documentation pretty much covers what you need to know. For most cases the library does little fudging between your app and the API behavior.
For the application I am coding, I use strictly STL strings, containers, and various Boost libraries. With WTL, I don't feel that I am paying for things I am not using like CStrings and such. For non-UI OS calls, I use ATL. In short, WTL, STL, & ATL let me produce efficient code without worrying about reinventing solutions.
One thing I am worried about is the future of WTL. Open-sourcing is great, but I don't know what direction the Windows API is heading. As .NET seeps deeper into the Windows Platform, I am afraid that MS is going to try to root out such a quick and painless way to whip out applications in unmanaged code. There's life in C++ yet, I just don't know if MS believes that.