Regarding take-home assignments, if you do decide to incorporate this into your hiring process, I think pulling a page out of Aaron Swartz's "How I Hire Programmers" [1] is a good place to start. Important points being to keep the task small and non-proprietary. If it is legally and financially possible, then also pay the programmer for her/his/they time.
[1] http://www.aaronsw.com/weblog/hiring