The four hours is my issue.  I don't understand how that is calculated.  Do I have to be posting for 4 hours?  Does reading count?  How/when does the tracker acknowledge that I have been on the site for a given period of time?  If I'm reading a long thread does the system timeout and I really only got 3 minutes of credit when I sat there reading over and over for 15 minutes?  A little clarification on that point would be nice.

I'd suggest whitelisting certain people.

Another option might be a non-spam bond; 0.1btc that you're not going to spam?