Facebook is about to force you into a Timeline, whether you like it or not.
You've probably run aground of Facebook's new Timeline format somewhere. Maybe you already opted in. If you haven't, click around to a few of your friends and you're bound to see someone's timeline (unless, that is — gasp! — you're not one of Facebook's 800 million or so users). If you like it, well good! You're about to use it. If not, well, uh… Well…
If you're already using Timeline, you can skip this paragraph. For the rest of you, it's going to become Facebook's default. Up front, it will make the back-catalog of your time on Facebook immediately available, organizing your activity by years and months. For the present, it'll suddenly look like you have two Facebook feeds presented willy-nilly, but there's a little line running up the center of the page — your timeline, if you will — but this is more or less a cosmetic change.
So, full disclosure, I haven't opted into Timeline yet, nor have I been asked to by Facebook. Not because I don't like it or anything, it just hasn't really grabbed me. If you want to get in early, you can head over to Facebook's timeline page and start customizing yours now. Or you can just wait until Facebook forces it on you in the coming weeks. Or you can just quit Facebook entirely. Whatever; the power is yours!
Bonus: If you're hoping to dodge some of the early hassles Timeline will present, CNET's Sharon Vaknin put together a nice little primer here.