I've used it for a long time with a blackberry and they never charged me...
I've been using it for a few days with android... no signs of any charges so far... It is a very popular app... the android community would let you know if anyone is getting charged...
i also used pdanet on palm and later blackberry however I couldn't get it to work on my droid x. I did get easy tether to work but only at 100 to 250 k . what speeds do others tether at?
I use EasyTether. Free to try but will not allow secure websites after a while unless you buy it, $9.95 US. I like it as it has Windows and Linux support.