I find it hard to believe that you did no extensive research on the existing sites in this category (i.e. your comment on www.billmonk). Some of the same features seem like a rip off of this site, but it could be a coincidence, so i will give you the benefit of the doubt, but they may not
Also, you really should contact them because they has patents on this idea according to their site. My roomate's old classmate from Northwestern Hugo Olliphant developed groupmoney.com --previously Gmoney.com
in 1998 in San francisco. The site has been up since at least 1999 and I have been using it in my groups ever since.
It is far more sophiticated and developed and easier to follow, has great graphics and is much clearer than yours. Yours seems confusing...very sterile graphic interface especially in trasactions category--looks like a blog page, not good. I like in Group money that they give you a whole bunch of the most used transactions (for roommates or other groups) by category with graphic icons--very user friendly and quick--- or you can add your own category
The site has in the past, partnered with paypal for payments and you used to be able to pay with credit cards although it was fee based for that. It apparently was dropped as well recently.
To settle, I usually use the "cash settlement" criteria to enter when people in my group pay up. I'm not sure why they dropped the pay pal feature they started in 2002, but it was not an option after about a year.