I have noticed that on the ASUS P5QL Pro motherboard the BIOS says "Dual Channel Asymmetric Mode" during POST. The motherboard has three 2GB Kingston ValueRAM 800 MHz DIMMs populated in the first 3 slots from the CPU socket. I have not run any benchmarks to verify that dual-channel is somehow being used, but I believed that dual-channel has to have an even number of sticks (and for triple channel, a multiple of 3).
Another example is the Intel DX58SO motherboard; it has four DIMM slots, yet it's an LGA 1366 motherboard which does triple-channel. Apparently triple-channel still works with four DIMMs, instead of falling back to dual-channel.
What does the BIOS' POST message mean in those case? Is dual-channel really used for the first two DIMMs, with the other one being an odd one in single-channel mode?