After 1.42 (Which clears up a HUGE number of bugs) the Permanent Potions add ten points to a stat.  I have yet to try on Mana or Stamina...
Just FYI to anyone who is interested <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />  
1.42 does not clear up a huge number of bugs; that was 1.40.  These are the fixes in 1.42, straight from the readme file:
   - Fixed upgrade mechanism for savegames from V1.4 that was broken in V1.41
   - Fixed problem with BF quest descriptions
...And as reported above, 1.42 breaks permanent potions.  There's only one left in the game.  Presumably, this will be fixed shortly.  Larian's been doing a good job of this.