I use joomla a lot and have been following the progress of something called Anahita Social Engine for Joomla (http://anahitapolis.com), which, like Dolphin 7, is in the "coming soon" stage. I will need to get rolling on my next project soon and at this point I think I will opt for whichever of the two is ready first. Anahita is talking December release. At the moment they have no demo available for the public, only screenshots, but the team definitely talks a good game and the project looks see more promising. I need to get rolling soon on my next project, and will probably opt for whichever is available first -- Dolphin 7 or Anahita -- as both appear suitable to my needs. My fallback is simply to build the site using Dolphin 6, although I guess that would be silly at this point. In any case, the relevant comparison is not Dolphin vs. Joomla (which is not by itself a social platform), but rather Dolphin vs. Anahita or Dolphin vs. JomSocial (which I have tried but wasn't thrilled with).