How does length affect power cable sound quality?

Wanted to bug y'all about a basic power cord question: How does the length of the cord affect sound quality? My gut says that shorter is better, but maybe there is some form a filtering required that makes length a necessity. For me, a standard 6 foot cable is estheticly 3 feet too long (at least--I could use some one and two foot cords).
Does an 8 footer sound better than a 6? is 10 better than 8? How much worse is 3 feet instead of 6?
In short, what is the optimum length, and how does sound quality suffer when that length is shortened or lenghened? Obviously, the exact type of cable used must be considered. Specificly I've ordered a "$200 msrp, $150 retail, cord for $50" for a Virtual Dynamics Power 3 Power cord, currently on AudiogoN, and available at that price for about 30 days, according to Rick.