I use my old GT mountain bike for errands and riding for fun. I put slick tires on it last year and rode several charity rides leading up to the Hotter N'Hell Hundred and finished the sucker. Not the fastest rig, but really reliable.
Last time we visited my wife's parents at their lake house, I ended up taking it with me to ride around. There's a monster hill on the way that is basically straight down one way and then straight up, with potholes and gravel at the bottom. I rode it several times, but after finding a safer line I let go of the brakes entirely. My bicycle computer isn't 100 percent accurate, but it's usually close. Here's a photo of my bike computer and the maximum speed (in mph) on the second line, recorded on one of those last downhill rides:
