Although Intel has been trying to obsolete the PCI bus in recent times with the Sandy Bridge desktop platforms not supporting the PCI bus natively, there are still an absolute ton of PCI slots available in the installed base and adding a PCI Gigabit Ethernet adapter is a very common use these days.
Two important notes about the Intel Pro/1000 GT card that are very important. First, the controller used is the Intel 82541PI. What this means is that ESXi 4.0 and later support is limited with it not being on the ESXi 4.0/ 4.1 HCL (although it does work for some users using the e1000 drivers). For those running legacy ESXi 3.5 installations, the card is supported, but I would not recommend picking one of these cards up if one is planning to build a VMware ESXi server at this point. On the other hand, the card does play nicely with Linux, FreeBSD (read FreeNAS) and Microsoft Windows operating systems so that is a major plus.
Personally, these cards work great for things like Untangle boxes. For example, I have a dual-core Intel Atom mITX box that had a free PCI slot. While it was being used as a music streaming endpoint, the PCI slot was rarely if ever used. Adding the Intel Pro/1000 GT along with the onboard gigabit LAN allowed me to build a very small Untangle box which works well.
The Intel Pro/1000 GT adapter works well, but one needs to be careful. As an aging piece of hardware (PCI based and the series that replaced the Intel Pro/1000 MT adapters) support is still there in most cases, but platforms such as ESXi 4.x which are known to be very picky about hardware are dropping support for the cards. On the other hand, the Intel Pro/1000 GT adapter costs approximately $30 new from Amazon.com‘s many sellers and around $20 on ebay. Personally, if one has a PCIe x1 slot, the Intel Desktop CT adapter is a much better option, but I do get asked about which PCI Gigabit Ethernet adapters I use regularly and I have a stack of these adapters that I use for projects like the Untangle server.
Feel free to discuss on the ServeTheHome.com Forums!