Megan's "Age Before Beauty" post is certainly true - older workers most definitely have a harder time landing a new job, particularly in a down economy. In my own industry (pharmaceuticals) I hear persistent stories of some of the large companies deliberately reworking the demographics of their work force in a way that brings this problem to mind.
The terminal degree for a scientist is a PhD. In most drug companies, that's the degree you'll need to have if you plan to have people reporting to you. A Master's degree, by contrast, will mean that much more time will elapse before you supervise others, if you ever do at all. Some companies are more willing to promote MS level people (eventually) to the same ranks as the PhDs (and thus have lab assistants report to them), while others have an impermeable ceiling that prevents this from ever happening. At any rate, years of experience will gradually raise the salaries of both groups, with the older Master's-degree scientists coming to earn a good deal more than entry-level hires with Doctorates.
And it's just these people, I'm told, that seem to have been affected by some recent rounds of drug company layoffs. The "old hands", particularly those without PhDs, appear to be getting culled disproportionately. "I guess they don't value experience", said one colleague of mine, after hearing from friends about what was happening. "Either that," I told him, "or they just feel that they're paying too much for it".
At least one large company looks to be bringing in new scientists at the same time it's letting older ones go, adding fuel to the talk about how they seem to have a target for their age and seniority ranges. If that's so, will all this have the desired effect? Well, it'll lower their salary and benefit costs, no doubt - at least until the next crop gets up to those levels. The effect on the research projects is harder to work out.