In the process of getting my first FG/SS bike.

I'm about 5'9'. Went to my LBS and tried out the 2008 Fuji Track and the guy sized me up and told me I should ride a 56 bike. I've been reading a ton of posts on here where people discuss their height and the size of the bike they ride. Seems there are a lot of people my height and taller who ride way smaller sizes (ex: 53 or so). I am probably going to go back and test ride the 54 but I was curious, is size that important, or can I simply adjust the different components if they don't feel right after riding my new bike for a while. Better to get too big or too small?

Cheers.