How many social media sites do you update on a regular basis?
Perhaps it would be better to rephrase the question as: How many social media sites would you like to update on a regular basis?
Ping.fm is a useful aggregation service which allows you to do just that: post content simultaneously to a large group of social media sites. It covers dozens of sites and includes these better known social networks:
With ping.fm, you can also direct an RSS blog feed to all of your social networks.
There are other services, such as the popular Twitter client Hootsuite, that allow you to post to the biggest social networks. But if your social media strategy involves reaching audiences on a diverse set of social networks, ping.fm is definitely worth a closer look.