When I started trading with Forex.com the I was under no illusion that I'd be paying more in spreads than I would from a commision based broker. My trades are medium term lasting from about 30 minutes to 3 days, so a few pips spread wasn't a big problem for me. Everything was going well so I decided to increase my account size. I was then trading with a $8000 account and that's when everything changed; delayed excecutions, fills at fake prices and slippage (which was always in their favour). On some occasions I saw 20 - 50pips slippage.
I could no longer make money with this broker so I closed my account. So if you want to trade demo then their demo account is great, but for real live trading look elsewhere.