Yes we use it in-house for testing. It is actively supported. I have reported bugs in Sikuli and have had tickets and workarounds suggested within days with the bugs fixed in the next revision.
It is quite stable. The problems I have encountered typically come from not specifying images correctly and the program selecting an incorrect area of the screen.
One of our more unique uses was creating a set of automated bench tests for a legacy embedded system. The system was written in assembly and had no unit testing capabilities. It communicated with a custom legacy PC application. Rather than try to locate the PC source code, reverse engineer the design, and then write some meaningful bench tests, we created a number of Sikuli scripts to interface with the PC app. It saved weeks of development.