I have a 2003 Nissan Altima 2.5 S and the service engine soon light came on right at 100,000 miles... it has performed flawlessly since day one. It has a small hesitation at take off but then immediately has its normal pep. I didn't take it in for the recall and was wondering if it could be that or something else? I have read about the fuel evaporative valve but it sure doesn't have a problem filling up. Any ideas?

There are lots of reasons in which you see engine service soon light. Check your vehicle manul for the detail. Do one thing, take your vehicle to the Sears Auto. They will check the your vehicle in free of cost and let you know the problem. Based on their diagnosis you can proceed. Also check if you have complain of rapidly lossing coolant.
It could be a transmission problem.
It could be head gasket blown proble if:
1. Overheating the engine(temp gause goes all the way high)
2. Could see while smoke
3.Rapid loss of coolant.

Many of the cars have a preset mileage that activates this light. On the earlier ones it came on at 80k miles for a smog systems check up. You can try to reset it by disconnecting the battery ground cable for several seconds and reconnect. The procedure for your model should be in the owner's manual or a "Haynes auto repair guide" for your car. Autozone may also have the info at the troubleshooting section of their website. Good luck