if you treat the demo with amazing seriousness...amazing seriousness...then you will learn from using it...if not...forget it and forget using it as it will just 'create illusions of trading grandeur'... obvious...if you treat the demo seriously and can't make money with the demo...forget trading with real cash-o-la $$$
I went from demo to small amounts of money to demo again. I find it's usefull to get a feel for a strategy with small amounts of money. I got to a point where I could respect my strategy, get in where I was supposed to, then exit on my stop manually without even needing a stop loss order. And still, I think my last 13 or 14 trades with real money were all consecutive losses. So, those who say that if you respect your strategy and cut your losses, that the profits will take care of themselves obviously never saw my account. LOL On top of that, backtesting showed the strategy was profitable. I laughed out loud when I read someone saying he was nervous about entering a trade even in a demo account after having losses with real money. I had some hesitation myself when I wanted to test my latest ideas. So, I think as long as you have experience with real money, it should be realistic to think you can still learn in a demo account. But, I'm talking about Forex which in my opinion may offer superior demo experience.
If you can have 'seriousness of steel' on a demo...than you can have 'success of reality' when you trade with real $$$ cash. remember...'perfect practice' makes 'perfect'...