Well, I thought it would be SND, very much theory, very little practical stuff (which you can do without having to buy the, new and expensive, equipment). But, since there is no official study material for the SND exam, it's a bit hard to determine the scope of the exam objectives.
It seems that anyone who has taken the other 4 exams already, find the SND a piece of cake because they already know all or most of it. Like going for CCNA after the 4 CCNP exams.
There is another important advantage to the SND exam, it is a 'core' exam for the Cisco Qualified Specialist certs. For example, for Cisco VPN specialist you need CCNA+SND+VPN exam. This also goes for the firewall and IPS exam. I.o.w. if you have CCNA, and want to complete the CCSP eventually, you can get three new certifications before completing the CCSP itself.www.techexams.net/ccsp/SND_642-551.shtml
It also depends on whether you have experience with one or more of Cisco's security products. I.e. if you have a good amount of experience with securing routers and switches, the SNRS exam may be much easier for you.