Check out the recipe in my profile called "The Kings Nutz". This is an imperial brown ale with maple syrup. Without looking at my notes, I think I used around 12oz. of pure maple syrup. The problem is...maple syrup is pretty fermentable. Most of the flavor is lost, but you do get a little bit through. I love the beer, but if you're going for an over the top maple flavor, you may want to try an extract. You could also try using the maple syrup at bottling time to replace the priming sugar. This might leave you with a little more flavor.