Mike,
We are using Dell PowerEdge R710 servers, Dual E5540 2.53 GHz processors with 8 Gigs RAM. The OS is on 2 mirrored drives, the video is stored on 3 RAID 5 drives.
Each server has about 40 Axis cams on them, all recording 1 FPS, switching to 8 FPS when motion is detected. Using server side motion detection. The cams are mostly recording at 1280 x 800. The processor rarely gets above 4%, we are using 2 servers only because we had 2 we were using for the previous VMS.
The software has been very reliable. We are on 5.5, I think they will release 6.0 this spring/summer. The Monitor Station is easy to install and configure, and also seems to be very reliable.
Their support has been great. Since they know we are still testing the software it is possible that this may change, but I am hoping this is not the case. Either way, we haven't needed much support once we were up and running.
They also have iOS apps that work well on iPhones and iPads, don't know if there is an Android version.
We have not even gotten close to maxing out the server capabilities with 40 cameras. When we move the rest of our cameras this summer we will probably go to virtual servers.
Hope this helps, please let me know if there is anything else I can help you with.