I've lived in Leesburg since 1999 and just went on the candlelight Christmas Tour last December (2012). First of all, you have to like history, but even if you don't, it is a beautiful house and very well decorated. They have a different theme, apparently, every year. The tour guides (young and old) are very knowledgeable of the house and its history, especially about the family that lived there. When I arrived at the carriage house (where you buy tickets/gift shop), they had hot cider and cookies available. The house is a short walk (uphill) from the carriage house.
Well worth the time and money, but not conducive to the physically handicapped due to the stairs. The entire tour took a little over an hour, but you could spend longer if you wanted. The grounds are lovely and I vowed to go back in the springtime this year, but didn't make it.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.