I was finally shamed into it by several of the MyITForum guys: I took the 70-401 certification exam, "TS: Microsoft System Center Configuration Manager 2007, Configuring", and yes, I passed with flying colors. I actually liked the exam: nothing too fancy, lots of questions around OS deployment (my favorite), troubleshooting, software distribution, software updates, network access protection, etc. Even though there are some portions that I rarely (if ever) do in my day job (e.g. network access protection, internet-facing clients, software updates, reporting) I still knew enough about the concepts and implementation to get the answers. Practical experience with the product is definitely required.
Now I need to figure out which exams to take next. I think it's time to look at the new Windows Server 2008 exams, working towards getting the "MCITP: Enterprise Administrator" certification, or maybe the 70-660 "TS: Windows Internals" exam.