This is my 13th year as a part-time mechanic. It's a fun job with it's ups and downs. The pay sucks and the hours are long. If you're good at what you do it's still rewarding and enjoyable. Here's some pros and cons of working at a shop:
Pro: You get to see and try out the newest and most expensive stuff.
Con: You have to work on the newest and most expensive stuff only to find it's very tempermental, requires special tools and is usually overpriced junk.
Pro: You have a access to high end bikes and components.
Con: You get to deal with customers that want high end components and bikes. They usually think they know more than you, buy everything from mail order catalogs anyway and are major buttstrokes.
Pro: You get to work on and sell some neat BMX and Freestyle bikes.
Con: You get to babysit all the local kids that have a million questions and no money.
Pro: You get to do what you really like to do, work on bikes.
Con: Most service bikes are filthy K-mart bikes that the customers want to work as well as that new Klein on the floor or something with the latest hydraulic disc brake setup that takes 4 hours to bleed and adjust.
Pro: You can purchase all kinds of kool cycling stuff at discounted prices.
Con: You have no time to ride.
Pro: A lot of shops sell fitness equipment. It's fun to assemble and try out.
Con: You have to unload and deliver some of the heaviest, most akward machinery ever made to peoples homes. (Usually a minimum of two flights of narrow, steep steps are involved.)
Pro: Selling bikes to casual riders and families is one of the best parts of the job.
Con: You get the JRA (just riding along) customer that thinks the bike his kid bent in half jumping from the roof of his house should be covered under warranty. He was just riding along when the whole bike imploded...
Pro: There are other "perks" like going to seminars and trade shows.
Con: Somebody has to stay behind and watch the shop. Guess who that somebody is....
Pro: If it's a family owned business you almost become part of the family and there's a certain bond between employees. You're not a number at a bike shop
Con: You can't get away with much. You're not a number at a bike shop.