We are now charging to post ads in our Personals section in most cities. It wasn't an easy decision for us to make, but we ultimately felt is was the only thing we could do to protect users and make the user experience more beneficial.
The spam was very heavy in Personals and very difficult for us to manage. After fielding many great user suggestions on how to deal with the problem, we found that users would like to pay a very small fee so that their ad would not get buried. 99% of spammers are not willing to pay to post their ads.
Users who post in Personals can now post with confidence knowing that their ads will not get buried under spam. Additionally, this lowers the likelihood of users responding to fake ads. We've also implemented a feature which allows users ads to stay online for 365 days in most Personal categories which means more bang for your buck (literally...a buck).
If you want to remain completely anonymous, get an AMEX or VISA gift card, which are sold at most grocery stores and online. They work just like credit and debit cards, only they are prepaid, and no personal data is attached to them.