In reply to wushu:
I would ignore the advice of both extreme camps above and instead think about the kind of riding you like to do before going SS.
This might help:
Against SS:
If you are all about going fast then SS may not be for you. Although people do ride them very fast most people feel a SS slows them down.
SS is harder work as there is no bail out gear option so good basic fitness is required (you'll build it pretty quick anyway)
Not ideal for really big hills although it is surprising what you can ride up SS.
Not ideal for large distances.
Not as versatile. People do use them for all sorts of stuff but...
For SS:
It's the cheapest way to get a light bike.
Low maintenance.
It makes you think about how you tackle climbs so it makes riding more interesting and makes you a better rider.
Simplicity is appealing.
It isn't nearly as hard work as some might have you believe.
You will get stronger.
IMHO SS is great but if I could only have one bike it wouldn't be SS. I don't personally know anyone who only has an SS but I know several people who have them predominantly for local jaunts.
Once you've gone SS and had a play with that finish the job and go fixed wheel...