For those who downloaded and played the demo version of Audiosurf, here's a bit of info.

After I downloaded it, I fired it up and was disappointed to see it not working. Firstly, some of the buttons were missing. After randomly clicking around a bit, I was able find the button that starts the level. Just to find that all the blocks were black.
As you can imagine, this is a problem. I tried different settings, restarting the game, editing the config files, etc. Nothing fixed it.
Finally on the forum I was able to find a bit of helpful info: Restart Steam.
After doing that the game was fixed, but when I tried to play a level, all my remaining demo songs were used up. This made me a bit upset so I developed a way to get past the demo counter.

To re-enable an expired demo, read further:

What you will need:

1. Downloaded and played Audiosurf at least once.
2. A Hexeditor. I prefer XVI32.
3. Locate the following file: $SteamFolder$\SteamApps\common\audiosurf\engine\Support\SavedConstants.cgr
4. Make a backup just in case.
5. Open the file with the hex editor.
6. Find the following address: $A398 (to make sure you have the right one (since some files might differ), it should have the text "FLVA" in front of it and a bit further up there should be a tag: "CHNA" containing a value of "NumNonRadioSongsExperienced". If the demo already expired, Address $A398 will have the hex value of 80 and the one after, $A399, 40.
7. Change both adresses to the Hex value of "FF".
8. Save.
9. Enjoy.

I was able to unlock some other characters by editing the file but they did not work correctly, so I won't include those here.