"If I go to a site with someone and we both find a silver quarter, that means if I had went alone I would have found two silver quarters."
That is the mindset of many solo detectorists, the ones that just don't believe in detecting with others. I used to be the same way. I was pleasantly surprised to find that detecting with others is not only more productive, but is much better than detecting alone for many other reasons. As a great detectorist named Jonathan J. put it, "More often than not, its the adventure, not the finds." And what's an adventure if you don't have anyone to share it with?
Also, detecting with a partner makes everything easier. Good partners share sites, share each other's personal network, share the burden of research and permission, and motivate each other to get out and detect more and detect harder. You can learn a lot by watching your partner and comparing your results with his after each session detecting together.
Here are some great places to meet detectorists and find a detecting buddy that is right for you:
The various online forums are great places to meet detectorists near you. Some forums will have a message board devoted to helping detectorists hook up with others in their area.
Some of the more popular forums are TreasureNet and Friendly Metal Detecting Forum. Many of the detector manufacturers also have their own forums, accessible from their websites.