This is an older thread, but I completely agree with Brian's summary of switches. Only $10 per port... I think that support for GigE is in the same category as management and really should be the default if at all possible. GigE provides several benefits that are often overlooked. Real network management setup and configuration like QoS, VLANs, STP, etc... can require more knowledge than most installers will have. Certainly the general field installer. However, now that Rapid Spanning Tree (RSTP), 802.3af/at PoE and 100/1000 Auto-negotiation is so reliable and easy to use, the default settings on many switches are good enough to keep you out of the ditch. I always tune things like that, but it is rarely if ever absolutely required...
•Cable Diagnostics - GigE switches today with almost any management ability are manufactured with the actual chip that touches each port capable of basic cable diagnostics. TDR, resistance, etc... That goes a long way toward trouble shooting the cable installation. 100Mbps switches do not usually offer this feature. They only need 2 of the 4 pairs of wires and cannot test them all. GigE uses all 4 pairs and generally can/will allow testing of the cables remotely.
•GigE bandwidth usually needs no managing in a small environment. Since most cameras are still 100Mbs, there is no way to saturate any link to the NVR which is usually GigE in a small environment. You still need to manage the bandwidth, but if a dark/snowy/rainy outdoor night scene causes several cameras to exceed what you are expecting and all you have is a 100Mbps switch for the NVR, the port can be so congested, that you cannot remote into it to understand the issue.
•IP Cameras are usually the slowest NIC you install. Except for very small printers or other ultra low bandwidth network attached devices, everything else you connect would be GigE. Routers, Access Points, Wireless Bridges (for connecting remote cameras), PCs, NVRs, NAS for archiving.... They would all generally be GigE.
If you REALLY are certain that the switch is never going to have to have anything but those 4 cameras installed and the NVR just lives on the same switch then fine. In a very tiny installation a small 100Mbps switch might be fine, but for long term support, and for a reliable/flexible installation, the few dollars more for GigE is well spent. Entry level web managed GigE PoE switches currently start at $10 per port. Only $10... That is less than the sales tax on each camera... Yes, we generally should know more about the network and correct installations methods. (This is IP Video after all..) Yes, we should understand camera bandwidth and the video settings to manage it, NVR storage parameters and reasonableness, Pixels per foot for images, Lux levels for image brightness clarity, lens choices for coverage, focus and stuff we all know at least a little about. (I still learn things every single day even after years of practice...) However, without all that knowledge or at least until we gain more of it, a simple managed PoE GigE switch can help save your project/customer from failure and give you insight in minutes that otherwise can take you hours. Also, keep a spare that you know works and learn to use it, just like you do UPS units, PoE injectors, cameras, crimp tools, cable wire testers, volt meters, etc... This was probably too long, but wired network bandwidth today is far too cheap to waste time on conserving this way. 10-20 years ago that was not true. Your time is worth much more to that to yourself, your customer and your friends/family. It just isn't cost effective to worry about 99% of the time. (This isn't true for wireless bandwidth, camera bandwidth, etc...) I am not saying to waste money or bandwidth, just spend the effort where it makes a difference.
Managed vs. Unmanaged, 100Mbps vs. GigE...
Those are not places to spend time arguing about at least to me... Spend your time/resources/etc.. where you can make a real difference to the customer. More time to train them, more time to understand their needs, more time engineer the NVR/NAS, more time to make it an attractive and functional system, etc... -scene from your office- Customer calls at 5:30 with a camera that is dropping out. It is your business, so you answered the phone even though it is after hours. You want to help, but they are across town and 5:30 traffic means it is 1-2 hours there and back in traffic. You just webbed into the switch, saw the port with some error counters that are not 0 and it is the camera port in question. So next you ran the cable test. The switch cable test says one pair is shorter than the others by the length of the 10 foot patch cable just installed last week... You asked them to just unplug and plug back in the camera cable that was not clicked in all the way. After the camera reboots it stays online without errors and stops dropping out. Customer is happy, you are happy... Happy emoticons :-) (emoji for you youngsters) all around.. Now go home and play ball with your kids, hug your spouse, have a beer with friends or do something else because you didn't worry about the $10 you had them spend. Just thoughts...