I've been running this for a few hours on a custom cooked ROM from SSK 1.5, running build 20954. So far no problems.
Install went perfectly, and I did set my settings the same as what was shown on the screenshot on the blog page.
I do use both Quickmenu and Opera Mini 4.2 and neither of them have had any adverse side effects.
I opened up WMP and played a few songs and there was never a stutter or lock up or anything like that.
I open the app settings and the current processor speed does drop down to 256 mhz after 5 seconds, and then when my screen dims it drops to 81.92 mhz. Tried this with music playing and the music went on uninterrupted. I don't have a good way to verify that it is doing what it says it does (no offense just saying I need to look into getting an app that measures battery usage or clockspeed outside of this app itself).
So far so good... hoping I see a nice boost to standby battery life with this... this is the first WinMo phone I've had that will drop 10-20% battery life just sitting in standby overnight if I forget to plug it in to charge it
EDIT: well the app definitely has control of the clock speed, when changed manually/manually overridden anyways! I set the manual override to 128 mhz, and immediately noticed the phones performance nosedive. Opened up TCPMP and went into settings, and it showed clock speed of 99 mhz (?). With the clockspeed left on automatic, and on the same settings screen in TCPMP, the clockspeed never changes (it always shows 530 mhz by default), but I don't know if this is just TCPMP just not updating this screen in real time.