There's a nice discussion over at Canadian Canoe Routes about ferry angles and paddling cross wind that just pure gold. John Winters has jumped in and given a good account of how to save energy using the right path. In the link below, go to page three.

I'll copy in some of what he wrote:

Imagine first that you are paddling directly across the wind to the opposite side of the lake and steering by compass. In this case you will end up to leeward of your target and will have to turn and paddle up wind to get there. Now imagine that you ignore your leeway and simply paddle towards you target changing your course to suit. You will hit your target and probably have paddled a curved course. Next imagine you paddle using your compass and have estimated your leeway correctly (you might do this in fog or in the dark if you paddle in those conditions). Now you will paddle straight course but with the boat always angled slightly to windward. All three techniques work. From a pure efficiency stand point the second method works best since you will constantly change course to adjust to conditions and maximize performance.