Using the dog park as a location for meeting potential dates has not worked out so well for me. In fact, I have not met a single person that I have been (romantically) interested in. I have noticed that the late afternoon visitors are more likely to be in my late twenty-something age range, but the few guys that I have been interested in (based on the looks of them and their dogs) have been sporting wedding rings.
Using the dog park as a general spot for meeting new people (with no hopes of future romance) has proven much more successful. I have made a small group of acquaintances with whom I meet a few times a week and have slowly gotten to know. These relationships have been fun to develop, as they are with individuals with whom I would be unlikely to get to know in any other capacity.
To all you singletons with canine pals (or even without), head for your local dog park and make some new friends. Perhaps you will have more luck than me and even find a date!