My new bike, finshed.

[laura*]

Also, hey, anyone have any ideas about what it means if the gears start skipping down when you pedal backwards? It only happens sometimes, but something got screwed up when the fenders were installed.

The rear wheel might be installed crooked - with the wheel pointing to the left.

When you pedal backwards, there is nothing to guide the chain onto the cassette cogs. (The rear derailleur only works in the forward direction.) Now assume you are cross chained in the big to big gear combination. The chain is forced through an extreme angle. Now increase the angle even further because of a crooked wheel. At this point the chain might not track backwards onto the current cog. Instead it will skip down.

There's a simple two part solution: 1 ) Don't cross chain, i.e. don't use the big to big and small to small gear combinations. 2 ) Loosen the quick release for the rear wheel. The wheel should have enough freedom of movement for you to center the tire between both sets of frame stays - both by the cranks, and also by your brakes. Once the wheel is centered, tighten the quick release without letting the wheel move.

The standard configuration is for the left hand to control the chain ring (front) derailleur, and for the right hand to control the rear derailleur. ... I would be very surprised to see any bike set up differently but I suppose anybody can make a mistake.

Maybe that's why it took so long to "install the fenders". The mechanic may have noticed their error and fixed it (switched the brifters*) without saying anything.

* If the left hand was controlling the rear derailleur, then the brifters must have been installed switched. Had the error been a cable misconnection, then the shifting wouldn't have worked properly. Of course, with switched brifters, the shift paddles would have been operating backwards.