I have... as few as possible. There are a few must-check's and a few more nice-to-have's.
Main capture - OmniFocus (desktop, laptop, iPad, iPhone)
Email - 8 different accounts (means I can just archive, no filing needed!) but all combined in Postbox
Twitter & Facebook - email notifications set up for replies, direct messages, etc., so that anything I NEED to see drops into my email inbox. If I fancy dropping into the websites, that's a just a nice-to-have
HelpDesk - book registration forms get processed on the website once a day, all other messages feed into my Postbox email accounts to be managed with email
Forums - my own forum I visit on the website, any other must-follow feed into a single gmail account for processing there, nice-to-follow are just buttons on my browser toolbar to check when I have spare time
Bookmarks - must-read go straight to OmniFocus, Pocket as nice-to-read-later stuff
RSS feeds - only nice-to-read stuff, Reeder/Google Reader