Before you freak out, listen to my first paragraph
I really like the idea of socalism/communism, everyone give what they want, only take what they need. However, notice I said the idea. Everyone knows that people are corrupt, greedy and selfish. This is, in a simple form, the current downfall of a classless society.
This, however didn't stop my thought experiment. What, I thought, could be done in the future to allievite this? Since I hal already identified money, power, and greed as the main factor that was currently causing a problem, why not project a future where that is gone. What you would need is a society where you not only had replicators, but where anything could be replicated.
First off everything would have to be replicated in a rather fast order; eg, you couldn't have a one year wait to replicate a starship. You can see some problems with this already -- what if someone wants something really big, like a space station? What you have to do then is place limits on what can be replicated. This is already the first breaking point, as people will still want these things, even though they can't have them. Second off we have the factor of control: say futuristic guns can be replicated instatenously. This will obviously be a big problem as most people wouldn't like others to have access to a large amount of guns. Therefore you would need control. This begins the problem of power. You can say, well, since this is the future, everyone can vote, and there is no corruption in the system. However, there is nothing to say that people can't convince others to vote for a way they want something. Right there you have the beginning of a class.
Hopefully this small thought experiment that I thought up over a weeks time or such is useful. In case of any *gasp* internal inconsistancies, feel free to elaborate!