If you pre-ordered Left 4 Dead from Gamestop or Steam, you should have gotten a demo code by now. If you didn't get one yet, you might need to fire off a few nastygrams. If you did get the demo, make sure you let us know how it is! I've yet to fire it up, as I'm knee deep in about 4 million other titles. F*ck you Fall Gaming Season.
On a lighter note, if you are sporting the Steam version of the game, you can utilize the new Steam Cloud service. This service allows you to store saved games as well as keyboard and graphics settings on Valve's servers so you can access them from any computer simply by logging into your Steam account. Sounds pretty awesome to me, makes me wonder why Xbox Live Gold doesn't have such a feature.