I think this is one battle mods can't seem to win. Formal, less formal, nah now you're not formal enough. PM, nah PMs are too formal, VMs are better, nah VMs are too public. There are so many directions that mods are being pulled in that it's probably better if they just went back to the beginning and started again.
Personally, I think mod PMs should increase in 'formality' as the PMs go on. First rulebreaks/new members = not very formal. Second = a bit more formal but still fairly informal. Third = formal