I've never heard of it, so I did a search. Looks like good ground cover. I'm including a link to Dave's garden website that has some comments about it. It seems it can grow under various conditions.

Kat

Here is a link that might be useful: Mazus retans

Are they hardy to zone 4? If you havent seen them growing around and about your area, its likely they are not.
I know I've not seen it in my zone 5 area. Sure is pretty tho. If you give it a try, let us know if it survives the winter.

Pondwelr, it sounds like flowerbrackob is already growing it. The link I had included above said it's hardy to zone 5. Maybe it's in one of those micro-climate spots.

Kat