pawsplay said:So friggin' what? You just pick an appropriate ethos to match the cleric you were going to play anyway.
Well - good clerics can't cast evil spells. Good wizards can. Good clerics who perform evil acts (assuming that their deity is good it is logical that this would be against the deity's code of conduct) will become (or at least in in danger of becoming if this is a consistent behaviour) ex-clerics (see listed penalties for that) as well as being subject to an alignment shift.
A good wizard who performs evil acts is subject to an alignment change but no loss of class abilities.
So it can very well be a big deal depending on how well the group is role-playing.