I just purchased an ASUS P7P55 LX motherboard, which supposedly supports up to 16GB of RAM, but after installing 4x 2GB of DDR3 G.Skill RAM, the BIOS reports 8184MB of RAM instead of the 8192MB that it should see. After setting up my system, I noticed this discrepency, so I ran MemTest86+. It detects all four 2GB sticks correctly, but says the total memory is 8181 MB. Despite this further discrepancy, I ran MemTest86+ for over 8 hours and no errors were detected. Does anybody have any ideas why the total MB reported is lower than the 8192MB I'd expect from my setup? 8MB may not be much, but I'm concerned it may be a symptom of some larger problem.

Does your motherboard have an integrated graphics chip? If so, the integrated GPU is probably reserving that 8 MB as a framebuffer...