Yes I have a Facebook account, but no I don't want everything I've been listening to posted up on there. So I've always been careful to ensure that "Show what I listen to on Facebook" is un-checked in Spotify's preferences. However having just gone onto Facebook for the first time in a few days, I see that one of Spotify's recent updates has sneakily re-enabled that option behind my back.
Just thought I'd post this as a warning to anyone who uses both Spotify and Facebook but who likes to keep the two separate. Of course if you've been a Spotify user from the days before it forced you to join through Facebook, this probably won't affect you.