There is a forum on this same board for plant ID's. If you don't get help here, try reposting there. They seem to know their stuff.

--McKenzie

where in the US is it growing?

Looks like a type of weedy Tradescantia...hard to tell what's going on with the flower.

You could go to the Name That Plant! forum to find quick and accurate identification regarding your plant.

Here is the link:
http://forums2.gardenweb.com/forums/namegal/?11246

this is called a "dayflower" where I live and I absolutely despise them, because they take over EVERYTHING.

Nc-crn and Desirai both have it. A tradescantia, often called dayflower or spiderwort. One of the few plants that has a true blue flower. It can be a pest, but my grandmother kept a bed of it in an out of the way spot where she wanted some color but didn't want to weed (she had extensive flower beds). It was very pretty bordered with orange touch-me-nots and it didn't require weeding since it squeezed out any other weeds.