We are lucky enough to live within driving distance to a LEGO store (well, maybe not so lucky on our credit card) so we end up visiting at least once a week. Yes, there are other places you can buy LEGO, like Toy's R Us (but they markup their LEGO so be aware of that when they go on "sale"), Target, Amazon etc... but the customer service at the LEGO store is fantastic.
The staff is in a word: amazing. Especially Daniel and Lauren. Lauren actually helped me feel through the various Series Minifigures packages, identifying different shapes. Great attitudes - especially when you consider how chaotic it can get in there (it's a kid mecca!), the burning lights (my only gripe) and now, the Holiday crowd, I'm always impressed by how friendly and helpful everyone is.
Also, be sure to join the VIP program. It's free to join and tracks your spending at the store - you get points for every purchase which you can use towards future purchases. If you're buying at the LEGO store and not on the VIP program, you're passing up free LEGO.
If you live in the Portland area, go!