Originally Posted by MG23
Newer Intel CPUs don't care that much; with 2+1GB in the same memory channel the first 2GB will be dual-channel and the last 1GB will be single-channel.
Older ones may have problems. No idea about AMD.
The channeling is within the motherboard chipset, and it only works when the adjacent memory modules in each channel match properly, hence the market for matched pairs of memory modules. Thus a 2+1 setup could harm the performance of the machine, as opposed to a 2+2 setup, even if only 3GB of it is used. It may of course be the case, that dual-channel operation has little or no impact in the OPs usage. My guess for media centre operation it doesn't matter, but not for the reasons you give.