Another petsite I frequent (PCE) changed the way their ads were handled a short while back. Instead of using an ad network that provides 3rd-party adverts - some of which can be malicious or inappropriate - users of the site pay a small fee to upload their own custom adverts for a specific time period.
This earns more than the pennies from page views on the 3rd-party ads, provides a safe browsing experience free from the threat of pop-up ads/malware/etc, helps the users who put up ads to get eyes on their stuff, and generally provides amusement instead of frustration. There are a fair few people who buy ads just to show off their pets! I think it's a fantastic model that more websites should get on board with, and I'd love to see Lorwolf be one of them.
The only cons I could see from this would be needing the time put together a set of rules for ads, and needing someone to moderate the ads to make sure no one tries to slip anything untoward in.
You could potentially pop in 1 free ad a month as an incentive to the membership as well.
Thoughts?