I've been running mine at 1Ghz for now 2 days. Zero abnormal symptoms so far. Been using it quite heavily also.

Last night, I was watching about 1 hour of Flash videos directly from youtube via MicroB browser.
Then watched about 30mins of xvid avi video via mplayer. Then played a bit of angry birds before I slept.
That's just the last 2 hours or so betfore I slept.
Then I plugged it into my PC's USB to let it charge overnight.
This morning, watched another 45mins straight of xvid avi file on the train.

But I don't expect everyone to have similar results. As I mentioned in my guide, I reckon only about 1/4 at best would actually be useable and stable at 1Ghz. Maybe I'm lucky. Maybe not. =P