I've had my new commuting hybrid for a month now (with no other bike experience other than in my teens 30 years ago). I haven't liked riding so far and other than being completely out of shape, I couldn't figure out why. The shop where I purchased the bike spent a few minutes adjusting the fit when I bought it, which I thought would be good enough for a beginner. But I just wasn't liking the ride: my wrists kind of hurt, my back ached mildly, and I just wasn't enjoying riding it that much. I basically felt OLD on the bike.
Then I spoke to a few of the office commuters and one suggested paying for a bike fitting. I thought it might be overkill for someone riding 15 miles a week, but decided I'd take a shot on potentially getting some improvement. That was an incredibly smart decision.
We ended up raising the seat about 3cm, moving the seat back on its rails 1.5cm, swapping my 7 degree/9cm stem for a 40 degree/7.5cm stem, and adding ergon grips.
Small adjustments, but I absolutely cannot believe what a HUGE difference it made. Zero pain, very comfortable, and best of all, I realized that before the adjustments, I was constantly thinking about the bike when I rode, and now I'm not.
Maybe if you're not such a bike novice, this is all easy for you to do yourselves based on "feel", but for me I am now an advocate of getting a professional bike fitting. Also, the Ergon grips are pure magic - every bike with a straight handlebar should have them (or something similiar).