They have a really good selection of high-end electronics. Back in 2002, when I bought my receiver, it wasn't available in any local stores. Crutchfield carried it, and they beat Crutchfield's price by $300. At the time, at least, I believe they were on commission, so they had incentive to barter.
However, since Amazon started carrying everything, and since Best Buy opened up their Magnolia stores, there's been more significant competition. Like Circuit City, they had financial trouble in the past few years (not THAT much trouble, since they're still around) and closed some stores in the St. Louis area.
Back then they had employees who actually knew the products they were selling, but I can't vouch for them nowadays. Still, it doesn't take much to exceed Best Buy's knowledge base.
No offense to those of you who work at BB and actually know what you're talking about. I know the discount makes it totally worth it.