I know you get this all the time, I saw 1-2 in these very forums but they don't really answer my questions. I have read through Before_You_Create_A_Network and I'm still on the fence.
I currently have 3 WordPress sites that I run. 2 are for my own site, I may add more later but for now I have my main site and another site on a sub-domain of my main site. They have different content and goals. My main site is mainly my own blog. I don't plan to generate a log of traffic there right away. My second site has been up for 2-3months and already gets about 7 views a day (great IMO). I may add more sites like the sub-domain site down the road (Like the way Lifehacker.com has sister sites.) Most of the sites will share a forum with categories for each site, I would like universal logins, I am using WP-Unite right now.
The third site I run is for another person who is doing their own thing and I just admin their blog and help them when needed. I might have a few more of those coming.
So should I look into multisite or not?