It's caused by native EFI/BIOS speed stepping in X230T. ML reads cpu state which is set on startup and can't change it later (especially when plugging in AC adaptor). See "Apple logo"->"This Mac" for CPU speed after booting with and without AC adaptor
Another news. My X230T is working with ML without any DSTS patches. Only thing that is not working well is sleep/wake function. I'm not using any VoodooHDA because it was causing problems with USB support (system was hanging).
Has anybody spotted ability to use USB ports in docking station?
EDIT (12.04.2013): Audio is partially working (speakers+jack working; mic dead; don't know about audio through DP, will try to check later) with AppleHDA linked by Freeman and VoodooHDA v2.8.0. I've read somewhere that it's the only one supporting ML x64. I've used the one in pkg file. The most important is no kernel panic and no usb problems