My opinion is - use them. I asked this same question once before and got smacked severely by some folks - but they need a life. Anywhoo -
Disneyland's official policy is to allow the use of FP anytime after the 'start' time (basically no expiration). At least that was the case when I checked last time I posted about this a few months ago. Disney World's position is 'no harm, no foul', basically leaving it up to the CM's. I had some give me a smirk and wink, and one lady who gave me a hard time but still let me use it. Our situation was a little different - trying to use it the next day as opposed to 2 yrs ago, but I know people who have used older FP's with success. You paid good money to get in the park, and if you didn't use the FP then, someone else had a shorter line. Kharma catches up - so maybe you'll get the spot of someone else who will use their FP in 2008!