Usually "shopping" questions are considered off topic in Stack Exchange sites, however in this site should there be an exception?
I think that if a user wants to know if, say a 4900 or 3400 is better suited for their particular config that is off topic. However, I think that we can suggest a particular technology that might work for them (qos, MPLS, etc) and then let them sort out the rest. The product lines move too fast to keep up with specifics.
I feel like things will often come down to specifics on manufacturers and even models. For example selection of a specific firewall to fulfil a specific set of traffic criteria, or quirks or bugs with certain switches that don't exist in other models.
Here is one "shopping" question already that doesn't seem out of place, if aything it's a candidate for community wiki page.
I would generally agree with Aaron above, but think there is something else to consider as well in that a certain set of questions may be on-topic. Again, I am inclined to give the benefit of the doubt.
I think we should draw the line at questions where a set of requirements are given, and where an answer is unlikely to be of future use as products change. In other words, I don't think it is enough that it is a shopping question. I think one has to look beyond that.
For example, "I am looking at problem X. Are there tools that exist or do I need to build my own?" strikes me as on-topic and re-usable. The models may come and go but if you get a few vendors listed it gives people a place to start looking and doing their own research. Even a vendor that has gone out of business provides a useful starting point if someone is stuck. For example, suppose you remember OpenS/Wan as IPSec management for Linux. You go and do a Google search for it and two things pop up immediately, that it is obsolete and no longer maintained and that StrongSwan is the replacement.
On the other hand, "What model of firewall should I buy given that I have the following needs" strikes me as non-reusable and off-topic.
So I would suggest treating shopping questions as potentially too localized rather than off-topic per se. For all the nominal rules, I also think this approach largely matches general practices on other SE sites. For example one can find all kinds of questions on StackOverflow asking for help finding libraries to accomplish various things.