One thing I wish this article had addressed is the memory issues invited by the “only once per turn” restriction. That clause makes it less easy to tell by looking whether an ability can be activated or not. The ability on [[Plague Nurse]], for example, really ought to require it to tap. Give it Vigilance, add the tap symbol, and remove the last sentence; it’ll be substantially the same card and the game state will be easier to keep track of.

I’m still mad that Planeswalkers don’t tap when you activate their once-per-turn abilities.