From what I've heard at my firm and from other people about their firms, it's not so much that the firms are in economic trouble right now, or that they're cutting back on growth. What seems to be happening is that firms are taking the "slowing economy" as an opportunity to "cut the fat." Firms tend to give more offers than less, and that means that a few years down the road, they have 3rd to 5th year associates who really aren't cutting it. They gave an offer to keep their offer percentage high for NALP stats, and they don't fire anyone b/c it hurts attrition rates, which clients are now starting to care about.
An economic slow down provides firms with the opportunity to get rid of people they probably would've "asked" to start looking for something else anyway.
IMO, I wouldn't worry about it now, but keep an ear to the ground over the summer. There are likely some firms who have been having growth problems anyway, and may really end up having some financial difficulty.