I've never actually known anyone with a 7-string or seen one played in-person. Personally, I'm confused by the concept. The extra bottom string is a B? So, how does one play chords and scales, basically, play the guitar? Do you tune the thing to E, or do have to tune it down, or to an open chord?

you tune the guitar B-E-A-D-G-B-E if you're tuning to standard. You could always drop-tune as usual and open-tune too... It allows you a lot of things that a 6 string won't, like extending arpeggios and scales without switching position, and limits some possibilities such as hendrix-thumb-over-the-neck chord fingering. Overall, I've been playing almost exclusively 7 strings for the past 6 or 7 years and couldn't go back to only playing 6 strings. Try one, you might have fun...