I have this unit aswell as the WPN111 (USB version) , I would say this is better than the USB version if you are going to keep it inplace , in the PC.
I found that the PCI version gives me better signal strength , and seems very very less prone to dropouts (when you place the antenna from both the PCI and USB in the same place behind the PC, obviously not installed at the same time!!). The USB is better as you can place the antenna with the lead supplied in a better place for reception and obviously the USB version can be used on other PC's if need be.
The bad point about this is that to update the drivers is a bit of a mess on , Netgear tell you to take the card out after uninstalling the old drivers , install the new drivers , then put the PCI card back in!!!!!!
With the USB (this also happens with the Siemens Gigaset 108 USB Adapter aswell) verison ,connections were dropping frequently when using other USB items like webcams etc , not due to power supply on the sockets (500mA on each USB connection) even tough they were kept apart using a totally seperate pair of sockets on the motherboard. Maybe my motherboard , or maybe USB bandwidth , I dunno!! Using the PCI version , there was no trouble at all.
Personally , I recommend the PCI version over the USB version.