Thanks, David. This was recently brought to our attention, and yes, real 8.x filers will panic, too. New-NaIgroup in the forthcoming Toolkit release will set the igroup type to "windows" if not otherwise specified.
Personally, I would prefer that the it either failed, or prompted for a response. Failing would be consistent with the CLI, prompting would be slightly more useful as it wouldn't stop a whole script running just for a small omission.
We have a lot of different LUNs, VMware, Windows & Linux, so defaulting to Windows wouldn't be the correct response for more than 50% of our responses.
Not specific to Powershell, but one of biggest annoyances with NetApp user interfaces at the moment is the lack of consistency! (e.g. useradmin user add vs CIFS shares -add!)