Is Organic Groups 7.x ready for production?
I've used OG6 in the past and am starting to use OG7 now for a website.  I'd say in general, both with the 6 and 7 versions that the learning curve in figuring out how to use Organic Groups can be steep for a newbie, since it's a complicated module with a lot of features, and a lot of related, supporting modules like OG menu, OG Extras, etc.

Give yourself time to play with all of those.  Don't expect to setup your perfect site in a day if you've never used it before.  It may be that the 6 folks who reviewed the module on the site you referenced had such expectations.  Also, those are 6 reviews out of over 24,000 sites currently using OG.  :-)  

My recommendation: do your own testing and make up your own mind before believing a review 100%.  Some of those reviews are probably quite valid, but OG is a useful module and may be able to do everything you want for your site.