I'm running just 1, but I'm making good money doing certain online work for marketing companies so I don't really have an ambition to start up a 2nd site yet.
Around 27 or so sites. Most are just sitting there waiting for me to develop them. My main ones would be Fireball Hosting and Wabuf - those two I can't live without.
I have 3 websits, 4 domains (two are similar domains pointing to one site). I only keep one site up-to-date so far though. Really should finish off my portfolio site and keep that up-to-date though.