Skype is spying us: the proof in this Interresting post (in french) explaining how to track system calls under linux made by a specific program.
Instructions use strace command (which can be replaced by ktrace -p process_id under os x).
In case you use ktrace, you may use kdump to parse the resulting log file.
To stop ktrace, either kill the attached process or use ktrace -C to stop all traces.