[puddleglum]

I like the idea of warming the oil. Ideally, I think both is the best way to go in cold weather. I have both fitted on my Rondo and it works quite well. I agree the oil will heat up the oil quicker and that is why you typically don't need as high wattage of heater for oil, but I think it will take longer to warm the entire engine. It will warm the entire engine by convection eventually (although I think the head would get warmer with a coolant heater) where as the block heater won't really warm up the oil. Having warm oil should cut down on cold start engine wear.
One of the biggest reasons for not using an oil pan pad heater IMO is the difficulty in mounting it. Wolverine insists their heaters have a flat mounting surface the size of the pad. That is tough to find on most modern cars and why I haven't put one on the Echo. Kat's heaters will allow you to bend the pad in one plain which helps, that is what I put on the Rondo. I wouldn't recommend leaving any of them on all day though.