Originally Posted by UT_Dude

You might as well do the easy double-check on the LBS... Take a ruler (customary, not metric), and lay it up against the chain. Each link (distance between pins) should be exactly 1/2 inch. Basically, measure the equivalent of 24 links (1 ruler length). If it goes more than 1/16" past the end of the ruler, your chain's bad. You can also buy tools that will check it without having to measure. I'd check that before i'd believe the mechanic... Shifting can go bad just from cable stretching, which is relatively easy and painless to fix.

As for learning to wrench.... This place is a good place to get started:

http://www.parktool.com/repair/

Or buy one of the Zinn and the art of whatever books. That's how I started only 6 months ago, and I already do everything on my bikes for far less time and money than an LBS would want. Higher quality repairs, in my mind, too!