Most of the top results for, real estate, are reciprocal link directories. Most of those also sell links. So I guess linkexchange is not very dangerous. Can we assume ontopic link exchange will remain safe forever?
Link exchange is not always a bad thing to do. It does improves your position in SERP's. The only thing that probably is good in one way link exchanges is that in those PR is passed only from one side and so the gain is both in terms of anchor text and PR. While is link exchange the gain is only in terms of anchor text and minimal in terms of PR.
This would be an old fashioned answer. Reals.com was banned a few days ago, and now it is on second page for an extremely hot term. We want to guess what happened, what might happen in future ..