Thanks for the info -- I have a large area near the northside (shady) of my house and the soil is crap. Every time it rains it hits the dirt and splashes it's magic all over my foundation and some raised planters. It's a wooded area near there and grass won't grow, nor do I want it to, so the invasive part doesn't bother me. My Grandma used to have Lily of the Valley and I like how robust the little plants are, thought it would be a good choice for this "rain buffer" idea. Thought of ajuga but it's taking too long to spread.
Pips seem to be a real bargain so I'll plant a lot of them.