FC provides all the information you need concerning offer expiration limits right in the FAQs:
Per the Terms of Service, offers and bonuses expire if not cashed out within 180 days of being credited.
We realize that this policy may be frustrating, but if we cannot "close out" accounts after a certain period, our accounting becomes unmanageable.
We feel that 180 days is an adequate time to cashout your funds, since the minimum for payment is low and you can easily reach it by completing no-credit-card-required offers.
The 180-day rule has to do with accounting procedures. It's nothing personal.
Many places will expire money credits due to accounting reasons. If you have ever gotten a check from a company (eg a rebate check, paycheck, etc.) they usually have written on the check that it expires in 90-days from date of issue. If they didn't do that, they might not be able to close the accounting loop and would lead to accounting nightmares. I think FC is being more than fair. Not only do they have this in their TOS, they also have it in their FAQ, they have warnings on your account page for any offer having less than 30-days before it expires, and searching the forum will bring up numerous threads on this topic. So I don't buy that this is somehow "hidden" when you signed up (you did agree that you read the TOS when you signed-up, afterall...)
I also think 180-days is pretty fair considering all of the ways to make money. As others have stated before, just by doing the PTC you can cashout within 180 days. If you are very diligent by doing the PTC, e-mail, and posting daily in the forum for that bonus as well as another bonuses (like the payment proof bonus) you can cashout within 90-days.
This past few weeks, I noticed that I was getting very close to having a bunch of my offers expiring (I slacked off with my work-load); I had to earn over $5 in about 15-days, and I didn't think I'd get the forum bonus from last month in time. So I went thru and did a bunch of surveys, and now I have only 56-cents to go (so I should be able to cashout by Saturday).
I do understand and feel sorry for those that run into problems (eg hospitalization, traveling to a parent's funeral, etc.) that occur which prevent you from getting onto FC. But other than that, I think the 180-days is fair. I actually could see some type of compromise. Like I said, I understand if there was something unexpected that came up, and so in that case it would be nice to be able to "freeze the timer" so to speak for a certain length of time until you get back on FC. So perhaps if there was some type of "personal leave" option that allowed you to freeze the timer on offers for, say, a week or two at a time. There'd have to be some type of challenge in order to earn this "personal leave", however, so that you wouldn't be able to use this option indefinitely. Perhaps every 180-days of activity (ie getting credited for an offer) earns you one week of "personal leave". Or maybe allow the person to take as many as they want (or perhaps limit to 5 between every cashout), but each time they do it means they need to earn an additional $1 in offers before they can cashout. That way people that do have issues out of their control can be given a little leeway to cashout in time, but it would still be difficult so that this option wouldn't be able to abuse the system.