Of course, whether this is useful to you depends on how you and your friends actually deal with money and small debts. With some of my friends, we use the "It'll all even out in the end" strategy. We'll take turns paying for dinner and events based on the "I think it's my turn" honor system.
With another group of friends, the bills are neatly tabulated and reckonings sent out by email for settlement. They use this system since they've known each other since college (I joined later), back when money was in short supply, and in order to accommodate group members of varying financial means. For this group, Bill Monk works great (and replaces a similar system some of us had set up to do exactly this).