The MPID address is the hash of a name so Hash(David) will contain the public key of (hopefully me) David, it is first come first served t the moment. There are options, but this one seems to mean it is first served.
It may be better to let folk use any name though pass their MPID name with that where the MPID name is a 64Byte number that is unique to them. The latter way is more secure and allows duplicate names as per facebook etc. Harder to find folk as they must have passed their ID somehow or you have been given it by somebody else.