I use localbitcoins.com and have done a transaction. I personally think it fulfills a vital role in the community. If you need to liquidate your bitcoins rapidly for some reason it's one of your only real options. As to the variance from current traded price and what they are charging, that has to be there to protect the parties to the sale from the volatility of the market. I can't speak for everyone, but I buy bitcoins based on the 24 weighted price. Think about it, when they place an order on the site the price is locked at whatever my formula says it should be at time of sale. Then it could take hours or even a day or two to finalize the sale in person. Meanwhile, I've taken cash from my account and carried it with me (along with my 10mil) to some coffee shop to make the trade. Going the other way I use current price + a hefty percentage because we all know the way this market goes by the time I get my cash the price is likely to be above what I'm being paid for them.