I agree with KnottedYet and Jolt. Buy something that you can, and want to, ride now. If you aren't comfy and happy on your bike today there's the possibility that you'll stop riding completely. That would be very, very, very bad!
When I was looking for my bike I wasn't sure if I'd like cycling or not so I didn't want to start out with a $1500 road bike. (Actually, I wasn't even sure that I could pedal for a mile.) I took a lot of things into consideration - living near the beach with bike trails that sometimes have a lot of sand on them, living near a rails-to-trails path, possibly riding with my parents, etc. I visited all 4 of the LBSs here and test rode a ton of bikes. Finally I narrowed it down to the Specialized Crossroads Womens Sport and the Trek Navigator 2.0 WSD. I bought the Crossroads and love it! It's perfect for sandy trails and the path that I like to ride on. The shocks/suspension keep me from getting too bumped around. It even works for trips to the pool on a pretty busy road. However, it's a heavy bike and I don't go fast.
I'm starting to want a road bike now. The way I look at is this: I will always have my current bike for knocking around on and in a little while I can buy a road bike for serious riding. And... If i can manage to fly on my current bike, I'll kick some serious tail once I get on something lighter and faster!
Good luck with your purchase and enjoy!
...May the wind be always at your back...
~old Irish blessing