You should look for specific reviews from your local store to develop a good opinion. However, in general, you're better off having your stuff installed at a shop than having "a buddy" do it, becuase they can be held accountable and your buddy can't. Basically, if it breaks, you just drive back to Circuit City and tell them to fix it. If your friend accidentally shatters your windshield with a screwdriver, you're plumb out of luck.
I would recommend going to google and typing in something like "circuit city (city name here) install" and seeing if you get any comments on message boards or review sites. Just know that for every negative comment online there are at leaste 100 un-reported positive experiences. Also, the free installation that they offer usually doesn't include the dash kit, antenna adaptor and wiring harness that'll be required, and they inflate the cost on this stuff sometimes. Find out if they'll allow you to bring your own parts, and if so, check ebay or versaspeed.com before paying Circuit City's price. If it's comparable, then go for it!
Finally, I certainly wouldn't advise against doing the install yourself. Even if you've never touched a stereo in your life, it's quite simple, especially if you use the how to in the tutorials section on this site:
http://www.nissanversa.org/tutorials.shtml Again, the only benefit to having it done at a shop is that you can hold them accountable for any mistakes.