I'm planning to go to SFWoA on Monday, and so I've been browsing Six Flags site for such important stuff as driving directions and ticket info. However, I've been completely befuddled about fast pass/lane/whatever you call it.
Six flags site does not seem to mention this service, so does it really exist?
If it does (as has been discussed) exactly where in the park can you get one? Is the "main office" as it has been described outside the park, inside the park, and if inside, where past hte first gate? Which gate should I go to to get there fastest?
Is a fastpass really necessary on a monday?
What rides should I get on it, at what times? Are the times assigned?
Is there anything else that I need to know?

Yes, it is real. You can buy one at the ticket booth and get to skip five lines of your choice that are availible with the fast pass. You can only skip certain lines though. Just remember the stares you will get when you take someone elses seat.

And I no, I don't think you need to buy a fast pass unless you plan to see sea world and go on rides.