I just did the fenders/rack thing this weekend. Time consuming, but not hard, but I also completely take my bikes apart and grease them when they need it.

I did have to get creative with some of the mounting hardware to make the rack level on the bike, but I am a little anal about stuff like that. The stays that are used to mount the rack to the bike had to be drilled so they would work properly.

I would reccomend using some type of thread locker on the bolts you are installing your rack/fenders that go into a brazed on fitting on the bike, but don't have a nut to keep things tight when you ride.

If you do attempt to do it yourself, then at least you will know how it went together and can keep tabs on it throughout it's life. Just take your time and be prepared to get creative to make things fit properly.

If you don't want to risk botching the install, then let your LBS tackle it. If they mess something up chances are they will make it right at no extra expense to you.

Good luck and let us know how it turns out.