Well, it is all about hte amount of control and configuration you want. If you just need more ports or bandwidth and it is a small office or community then you might be able to get away with non-managed switches. I worked for a medium sized (2 locations, 150-200 employees)call-center for several years and even with alot of VoIP traffic along with all of our applications being web-based they would never upgrade to managed switches are were just using standard 24 port 10/100 Netgear switches. They could never justify the cost.
But if you are in an environment that you need to segregate traffic, monitor bandwidth, or need any other statistics or monitoring capabilities then I would suggest investing in managed switches. That doesn't mean every switch needs to be managed, but at least the main one or two just so you can monitor that core. With managed cisco switches it allows you to turn on SPAN (setup monitoring ports to sniffers), watch the amount of bandwidth per port, statically configure ports instead of auto-negotiation, EtherChannel, tweak Spanning-Tree Protocol, and many more things.
The major factor for most small buisnesses is cost. If you chose a managed switch then you will pay much more. And although there are lots of options you probably won't use in a managed switch it just matters on how much downtime you can afford on your network. From my work at the call-center the network was frequently rampaged with worms and small viruses and it always required downtime to find the source of the problem and fix it. In a web-based buisness that was critical downtime, in my opinion (the IT direcotr didn't see it that way and therefore would never upgrade).
Its all about cost vs configuration. If you give more details on your situation and environment then I'm sure the community here can come up with your answer, or at least an educated recommendation, as to what you should do.
Let me know if this helps.
Burke
