This seems like a good place to share something I discovered this past summer:

After 8000 miles on my Madone, I was getting a loud squeak every time I shifted into the big ring. I put the bike on the workstand and traced the noise to the plastic guide block that attaches under the bottom bracket. The block acts as a guide for the front and rear derailleur cables. I assumed that because this was a nylon block it needed no lubrication. Not so! Both cables had high friction where they passed over the block. I turned the bike over and put a few drops of chain lube on the area. The difference was huge. The bike shifts effortlessly now, just like when it was new. Upshifts require much less force on the shift lever, and downshifts are much faster.

-Adam Molny