Actually people laugh when they see a completely unbacked thing being called currency
There's nothing wrong with an unbacked currency if everyone understands the rules going in to it - instead of being backed by the bullets of a government (which is the only thing the USD is backed by anymore), Bitcoin is simply backed by the voluntary acceptance of it by others. The fact that there's a huge chunk of those "others" who are accepting it at what could be vastly inflated prices, based on the speculation that if it takes off "it's going to be huge" doesn't really say anything about an unbacked currency, it merely says something about those others' "investment" decision making process.
There is a tiny "economy" going on... a handful of businesses are accepting Bitcoins (at huge risk at the moment, due to the above-mentioned price factors), and there are several trading sites where people have actually sold shit to each other using Bitcoins. I've sold stuff using Bitcoins - it's nice to know that once I pass the finish line (USD in my bank account for me, I can't pay my bills in BTC), I don't have to worry about some shithead doing a chargeback on something I can't recover. To scoff and not call that an economy is just being stubborn and silly.
I think I know the other place you're discussing Bitcoin, and I'd just like to point out that it's detractors are for the most part, just as big tools
as Bitcoin's biggest cheerleaders. 95% of that gargantuan thread is people making idiotic assertions that are patently false, that anyone who spent 5 minutes looking over the wiki would already understand are already addressed. But no, I enjoy reading 80 times a day "what's stopping satoshi from making more coins at random?" as much as you probably enjoy reading asshats talking about how Bitcoin will change the world if only someone else does the hard work of bootstrapping a real economy to match it's speculative worth (and don't even get me started on the - now thankfully thinning - libertarded approach to tax dodging using BTC as a selling point).
There are real, intelligent concerns to be had about Bitcoin's legitimacy as a real currency in the next decade or two (though hopefully not insurmountable, time will tell) - but if you guys think you're hitting the nail on the head with "hurr, not backed by anything", as I said, just as much tools as the BTC cheerleaders.