tell application "Contacts"
repeat 50 times
set theGroup to group "MyGroupName"
It's a crude hack. I had to change "MyGroupName" five times, and when the replicant count dropped I had to reduce the repeat number so it would execute. (One could drop the count parameter and see if the repeat loop stops when it errors with "missing value"; that would be much faster. I was being cautious.)
At one point Contacts didn't respond very well. I quit and restarted and completed the process.
When I was done I confirmed iCloud's web view was also Group free. Then I purged all the Contacts in that account , it's now pristine.
I'm sure an AppleScripter could turn this into a general script for removing all groups all at once. Or could get very clever, and only remove groups that had no contacts (so one could salvage the group/contact relationships).
I didn't need that. My problem has been fixed.
Incidentally, I think iCloud sync works a lot better in ML than Lion. iCloud updated very quickly.
 I have 4 AppleIDs. Two or three of them have iCloud accounts. One has all of my iTunes and AppStore purchases. One was my MobileMe account. A third, which I've never used, acquired, apparently by email transfer, all of my Apple device records. Does Apple have any idea how screwed up their AppleID/iCloud accounts are?
 Of which Jamie Zawinski wrote: "I used to think that PHP was the biggest, stinkiest dump that the computer industry had taken on my life in a decade. Then I started needing to do things that could only be accomplished in AppleScript."
 They're safe in Snow Leopard until I move my primary machine to Mountain -- which might be sooner than expected. ML seems to be everything Lion should have been.