When utilizing a kegerator, or home draft beer system, you must keep the temperature of your kegs uniform at all times. It is a good idea to keep a thermometer in your kegerator at all times and be prepared to adjust the cooling when necessary. It is well known in Ireland that if Guinness goes through too many temperature changes, it affects the flavor dramatically, and the same goes for almost all fine ales, but especially the darker varieties such as stout, porter, and barley wines.
38 degrees Fahrenheit is the optimal temperature for storing and serving most ales, and applies whether the beer is a domestic beer or an imported one. Also, whether or not the draft beer is pasteurized, it should be maintained at this same temperature. Part of the reason of this is that as the beer increased in temperature, CO2 is expelled from the liquid-gas mixture. This causes extra foam as a result, which most of us have had to deal with as part of tending a keg.
If you are force carbonating a keg of beer (i.e., by means of CO2 gas instead of natural carbonation), it is always wise to store the keg in your kegerator. The lowered temperature allows easier absorption of the gas into the ale, which will ensure that your keg does not erupt in foam as result of the force carbonation process. You can lose up to 25% of the beer in a keg as a result of foaming, so it is very important to accurately control the carbonation situation.
Timing is very important in the serving of refrigerated beer. A keg should be refrigerated at least as much as overnight before being served. This will allow the temperature to lower from room temp. to the regulation 38 degrees. Putting the keg in the kegerator even four hours before tapping it will cost you much beer in the form of undrinkable foam. It is probably a good idea to lower the cooling factor of your kegerator if you are trying to cool a keg in less than ten hours. As long as the beer does not become frozen, it should be fine. Some people report that too-cold beer causes bloating and burping, but it is always better too cold than not cold enough. Who doesn't find tantalizing the often advertised phrase "Coldest Beer in Town!"
All of this makes it necessary for the home bar operator to ensure that the seal upon his or her kegerator in maintained well. Many kegerators I have seen come with padlock hasps to ensure that the kegs within maintain their integrity. This is also handy to ensure that those without the key to the padlock cannot access the beer or brews contained within.
If you are buying kegs at a store or at your local microbrewery, I advise you to take every precaution to ensure as little temperature change as possible is effected upon the beer. Make sure that you will be driving in a traffic free time or route. Call ahead of time to ensure that the beer keg has been chilled overnight, and will be at optimal temperature when you arrive to pick it up, and have your kegerator nice and cold and ready to receive the brew upon your arrival.
By following all of these precautions, you will certainly ensure that your home draft beer system is operating at maximum efficiency. It doesn't take much more than a little planning, though, so don't sweat it. Just be prepared to keep your beer nice and cold, with as little interruption in the process as possible.