hansel

fixed is so much more fun the ss. Like sebster said you just feel connected to the bike. I also run clipless so i feel like im literally connected to the bike. Its a great way to switch up training for the road and i feel like it makes you a better rider. If your doing a hilly century i would go ss, although i love going up hills cranking such a big gear. Going down is a different story i had to get off the bike today because my legs themselves couldn't slow me enough. I only got off once and walked it for about 40 feet. but after that you get used to slowing and anticipating the downhills. you can always just get a flipflop or two separate rear wheels one fixed one coaster.

i also agree that a fixed drivetrain will help on the flats, you can take little brakes and just let the bike spin, and you retain most of your speed as long as your tires aren't crap.