I've setup another post about building a communtiy. I need some software for social networking, but need to be able to customize it on a fairly large scale. What are the current leading brands?
Are you asking for something along the lines of a program that manages your social networking accounts on a mass scale?
I used Joomla CMS Component called Community Builder for my social networks and it was good... if it that your question
If you don't mind to spend some money and want to save lots of headache, you could set up a network in Ning. For 20 per month, you could run your own ads on the network and just $5 on top of that, you can mask their networks' url.
Try Converting Drupal into a Social Network. If you really want to scaleup thats the best option. But it involves development cost. I think you don't mind spending for developing a large social network. You can also try joomla with community builder. If you want something for very cheap, you can go for Boonex Dolphin. Their latest version seems to be really good. You can also scale this to a reasonable level.
Although primarily a forum software, I recommend SMF (Simple Machines Forums). Tonnes of mods to build a community, free and open source, a great community itself to help you on your way, it's just great. http://www.simplemachines.org/
If you like you can use WP with many social plugin (buddy press) or WP MU if you have more cost you can use Social engine and many more plugin like Blog, forum, groub, and many more like Facebook... or if you want to make a social bookmarking site pligg is the best ... @tradester i mention it bro