I have to agree with Celt,
I wear the tartan of the clan I am related to, as well as Black Watch & Scottish National, as those are acceptable as well. I would not (personally) wear a tartan of another clan without darn good reason.

I admit I am a bit jaded here, I was a member of the Army 82nd Airborne, and wore the Maroon beret with great pride, knowing I had earned the right to do so. I aspired to one day prove myself and don the Black beret of the Rangers. Things changed, the black beret lost it's meaning and one day I showed up and was simply issued one, and I will admit, that I feel no pride in wearing it.

Im not bashing those with no Scot or Clan affiliation, to me that opens up a whole lot of choices for you regarding what you wear, my choice is to have some meaning behind my actions, thats all.
Theres a good feeling when there is a bit of pride and meaning in anything we do.
Just my 2 cents.

Keep kiltin',
John