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I'd say the minor amount of water underneath the oil filler cap is probably just condensation. A 2 mile trip probably isn't quite enough to get everything warmed up and drive out all the moisture. If there is a coolant leak into the oil (i.e. blown headgasket) the oil on the dipstick will eventually turn into chocolate milk - then you need to worry about it. Often - if leaks occur between the one oil passage in the head and the water jacket the oil will flow into the water (50-60 oil PSI vs. 10 coolant PSI) - look under the radiator cap and see if the coolant is oily. As Matt suggested - taking it on a longer drive once a week is a good idea.

Other problems which may arise from being driven too gently for short distances are:
1) carbon buildup in the cylinders - once warm - accelerate hard through the gears once or twice every couple of weeks
2) moisture buildup in the brake calipers - once a week or so the brakes need to get heated up enough to drive the moisture out of the calipers - otherwise they are much more likely to rust and sieze.
3) corrosive buildup in the exhaust system - a brief drive won't warm up the system and corrosive gasses condense from the exhaust. They will rust out the exhaust system unless the car is driven far enough to warm up the entire exhaust system and drive out the vapors.