There is an interesting thread at WebmasterWorld that asks, "What can you do when Google doesn't act on spam reports?" Here are some of the feasible actions one can take, that were mentioned in the thread.
- Strengthen your own site
- File a DMCA complaint with Google, they must act on those
- This idea may be a bit too nasty for some
- Here is a more detailed approach to filing a DMCA request
Forum discussion at WebmasterWorld.