one guy at my LBS took my valve covers off and pitched em, one guy told me to Always cover my valve stems. He said it protects them from the every day bumps and grinds of the road not to mention the bike falling over into bushes, hitting a pothole - you know - the things we would NEVER do to our bikes. Just call me Goofy but I think it helps to keep the valve stem screwed in also, I know...sounds weird but I had a big problem with a valve stem that kept coming loose (Specialized tubes) until I started using the caps.

Lise: congrats on your very quick and successful tire change. Bikemom is right - even with the front tire I just flip my bike upside down to work on the tires. Then I don't have to deal with figuring out what to do with the bike while I"m changing my flat - again! (6 tubes and 3 tires in 4 days...oh yeah...my life rocks right now! ROFL)