I took the CDSA certification in December 2010, about 5 months before graduation, and after I had finished the required courses in my undergraduate software engineering degree program. As soon as I have the recommended experience, I'll be sitting for the CSDP certification as well.
Overall, I feel these certificates are among the best for a software engineer. They are rooted in the Software Engineering Body of Knowledge, which was developed by people from a number of organizations around the world to identify the key knowledge areas for a software engineer. It's offered by a world-wide respected organization, and that right there adds even more value to the certification. These certifications also correspond well to not only what I learned in the classroom, but the skills that I've used or seen used on projects at a number of organizations.
In short, yes, these are legitimate, well written, certificate exams.
I think my answer to a related question about the CSDP certification is of value.
A few key thoughts from that answer:
Like any certificate, it's only proof that you know certain topics, by the book form. They don't really say much about how you'll perform on-the-job. Your past work history will do that far more effectively.
How employers view certificates varies widely, between industries and organizations. Some industries favor certain certifications over others. Organizations also place their own weight toward perspective employees and the certificates they hold.