Brisbanes have lots of things weird at all multipliers. In short, it seems to downclock RAM when you use any kind of divider, and it will also occasionally downclock RAM using the 1:1 ratio at certain multipliers.
It doesn't really affect the OCing experience negatively unless your board has little HTT headroom. You can always run your memory at 1:1 with tight timings and crank the HTT if you're having problems properly balancing CPU speed with memory speed. However, you can usually hit a memory speed that's good for your current OC with a ratio like 3:4 or 2:3, and you can tweak the speed with your CPU multiplier and/or the HTT bus once you figure out how it all works. An X2-3600+ Brisbane seems to run your memory at x% of its projected speed, where x = 10 * CPU multiplier, unless you're using the 1:1 ratio, in which case you get the normal speed for your RAM usually . . . I think. Honestly I'd have to go back and do more testing to make sure about which multipliers work well at 1:1 and which still penalize you (and to what extent).