I've had this lying around for a while, thought I might as well release it.
(You'll need to add PS3TMAPI_NET.dll into your project!)

So here is the function:

    

        public static bool VerifyMAC() {

            System.Net.WebClient WC = new WebClient();

            string MAC;

            PS3TMAPI.GetMACAddress(0, out MAC);

            if (WC.DownloadString("Put pastebin link here..").Contains(MAC))

                return true;

            else

                return false;                 

        }

/*

if (VerifyMAC())

    MessageBox.Show("Accepted");

else

    Application.Exit();

*/

You'll need to create a pastebin containing your mac address as a verification type system
(obvious using a mac address verification system isn't very safe because it can be changed)

Here is a example

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edit:
Where it's got
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Press RAW and get the link from that and then put it where it says to in VerifyMAC()

Credits to Sony for making the PS3TMAPI Library/SDK