Great to hear from another Davy who is interested in the DNA testing! .. My lot are from Wales and Devon (emigrated to Australia and New Zealand). I don't know of an American link per se, but who knows?
It's a pretty painless procedure, just send away for a kit (I used 'family tree DNA' see:http://www.familytreedna.com/
..when it arrives swab the inside of your cheek with the cotton bud, put it in the plastic container provided and send it back in the reply paid envelope. Wait a few weeks and they post you your results (and matches). You can send it anonymously if you like, with name hidden.
For male line, use the "Y-DNA" test (starts around $70 for a basic test (12 markers) but they do recommend 37 markers if possible (around $150 I think). It is a shame it's so expensive, but I think compared to all the money I've spent searching on sites like ancestry and sending away for paper records .. it's probably not too bad.
All the best, if you decide to go ahead with the testing I'd be happy to compare results. There are around 10 other Davy men on FTDNA database so far.. unfortunately I don't match with any yet, but you may have better luck than me.