First, I assume you are speaking about divs, right? Layers were a short lived and never standard Netscape proprietary approach.
Harmful? Well, I was backed into a corner once by a CMS and had to do it. And I can say yes, there's a downside for search engines in the following ways:
1. All the detailed information ends up on one url, so you can miss out on a lot of search terms that way, especially those down on that "long tail".
2. The html files size gets pretty big. At least stastically search results seem to feature the smaller file size pages. Of course that's not a direct "cause and effect" thing, but it does seem to be a correlation.
I much prefer other approaches, say, separate pages, and even informational pop-ups, rather than showing and hiding substantial divs.
Yes, you will see dHTML divs on Yahoo and Google. But they have no issues getting search traffic (especially gMail!)