I've been using By Terry's Terrybly for a while now. It's the most expensive mascara I've ever bought (I think it was about £32 or $50)....I was drawn in by a Space NK assistant who told me all sorts of amazing things about how good it is for lash health, but frankly haven't noticed any difference in "lash quality", and the mascara itself, while very good, is only on par with Benefit, Dior and Estee Lauder products I've used previously. I wouldn't really recommend it - not because it's a bad product, but because I feel it's drastically overpriced. I'll be going back to Dior once I use it up.
Or getting suckered into something else because of clever sales tactics...