How is CiviCRM in a Drupal Commons Install?
There would be no conflicts. I think the question of what makes a good drupal 'social community' is a specific drupal question and should be asked on that StackExchange, however if you want more specific answers here it would be helpful if you clarify in your question what you want the system to offer users. 

Having used Commons once (due to someone elses choices) but eg Organic Groups many times, I would not opt for a pre-built system like Commons. But again that is not a discussion for CiviCRM SE really.