As mentioned by other posters, it really depends if the work was performed up to code. I've attempted to purchase a property that had unpermitted additions added and was told by the inspector that those additions (in this case the entire second story of the home) would need to be ripped off/torn down and rebuilt to code before a Certificate of Occupancy would be issued. I'd definately look into it asap to avoid any possible surprises in the future.

You can expect an inspection and likely a fine, or if the inspector really wants to make an issue of it - worse. If you feel confident the work was up to code, I would recommend you just leave it alone.
This is not likely to affect your resale. Everyone *should* pull permits all the time, but honestly - it doesnt always happen.
Next time - pull a permit first.

Pat
The real issue is this - was the work performed to code? If the work was performed to code, then not having a permit is not as large an issue. The problem most people have is that when work is not permitted, the contractor can take shortcuts that they otherwise would not be to take.

The real cost will be if the building inspector requires you to correct things in order to issue the permit.

Good luck.

In the town I live in there is a fine and an inspection. I would definitely start the process now because sometimes it take a long time, and it can hold up a closing or worse, the buyer can walk.