Amazon with their free shipping and 37% discounts I'm sure remains a very real competitor, so there's that.
Not for singles. Amazon still hasn't tried that market (no idea if they ever will). For trades, it still depends. They do better then DCBS for IDW that's for sure (because they still haven't bumped it up to 40% off like the rest of the front of the catalog. Which they really should do by now!) And sometimes they might best a price for a Dark Horse book that's rare. They usually come very close to matching it.
As for Amazon's free shipping, the bump up to $35 minimum to get it really pissed a lot of people off.