Where Does Mitt Romney Live?

I missed this tid-bit over the weekend:
Despite selling his only home in Massachusetts, former Gov. Mitt Romney (R) voted last month in the state's Republican primary to choose a candidate for Sen. Ted Kennedy's seat using his son's address and has already mailed in a ballot for the Jan. 19 special election.

Romney spokesman Eric Fehrnstrom said despite selling his home in Belmont last year, Romney never gave up his Massachusetts residency. When he is in the state he stays with his son Tagg.


TPM checked in with Fehrnstrom after speaking with the town clerk in Belmont, Mass., who confirmed that Romney voted in the Dec. 8 special election.

He used an address in Belmont that matches the address of a home where their son Tagg lives.
Exit question: can you do that? Can a person vote in a state election if they do not have a permanent residence in that state? Any lawyer-types out there who can shed some proverbial light?