I've also been off for quite some time now (I "deleted" my account 3 years ago). I know none of the information gets removed so I logged back on early last year to grab some old pictures for a wedding slideshow. It's really scary how much I wanted to keep it activated after re-activating it, and how quickly people started messaging me about why I was back on Facebook. I'd say it's less like the plague and more like gangrene.