autozone will check the code for you, and i'm not sure if they are technically allowed to turn it off for you (i went today and they didn't) but you can at least do it yourself if you can get your hands on the controller (i've done it before)
majority of CELS are related to Emissions problems and usually aren't very serious - but don't neglect. if the car is running ok, then obviously it's something that may need to be looked at eventually, if symptoms occur.
I have had Phantom CELs in the past that don't leave any codes to be read. To reset the CEL you can disconnect your battery for a time and then reconnect. Make sure you have your radio code before doing this
As Jads says, if you want to reset yourself, disconnect the battery for at least an hour, having to hand the code for your stock radio. This will rid the light for the while but not its cause. I understand the light will extinguish itself after 10 start cycles.
Check all vacuum lines for security and splits, especially around the throttle housing.