Yes i looked them.
That controls are powerful. There's even a tool to draw forms that's incredibly similar to Delphi
The only problem i've found is some lack of documentation. For example i'd like a demo/tutorial on skinning, and also some information to use sdlcontrol with other program, ie integrating them in existing games/programs.

Also, i've had some problem in with cross platform compatibility, but i finally got them working on both linux and windows.