You will hear a whole range of opinion on this subject. I use my BD Lighthouse and Firstlight Tents in generally Alpine conditions in the Pacific Northwest and Sierra. They've never leaked. The Lighthouse, in particular, over the last 2 1/2 years, has withstood several multi-hour bouts w/ rain w/o leaking. As Winter fast and light tents, they are superb. I've heard of people having trouble w/ Epic canopied shelters in lower altitude, warmer, humid conditions---mostly condensation issues.
BD is careful not to call Epic as anything more than highly water resistant. Some people have had experiences like mine. Other's have indicated that they have leaked under far less severe conditions.
Epic, one should know, will readily leak if it gets dirty. However, cleaning it restores it's original qualities. I have field cleaned my tents w/ water and cloth sucessfully.