Well I'd say that previous experience is helpful, but not neccessary. Passion on the other hand is crucial.
My personal experience -
My wife and I just opened our first Coffee Bar, Muddy Waters Coffee Bar, in Charleston, SC a little over three weeks ago. Neither of us had pervious coffee industry or barrista experience before we decided to open an espresso bar. We both loved coffee though, and knew what great espresso drinks should taste like.
Before we opened we did some 'crash course' training with our roaster (Counter Culture out of North Carolina - a great outfit!) and my wife 'volunteered' at a local independent coffee shop for three weeks to get some hands on experience. We do things completely different from the cafe' she voluntered at, but just having here get used to the work flow and pace of business helped alot.
That was enough to get us started, the rest we're learning hour by hour, day by day and so far things are going pretty well for us. I know not every drink is made to perfection (which bugs the hell out of me since I'm a bit of a perfectionist), but we are committed to constant improvement and truely want to be the best. We will get there!
So, don't let your lack of experience scuttle your dream if you really love coffee, love people and don't mind working 7 days a week!
Oh yeah, no matter how well you try to forecast profit margins, traffic, cost and time to get the business up and running, etc....all of it turns out to simply be wild guesses once you get open!
George Worthington
Owner - Muddy Waters Coffee Bar
1739 Maybank Highway
Charleston, SC 29412
http://www.muddywaterscoffee.com (not up yet)