Oh, are the lines refrigerated or otherwise thermally controlled? I always presumed it was regular tapwater; i.e. probably slightly below room temp, but not much.

Mileage obviously varies, but the "beer nerd/snob" bars I've been to simply don't re-use glasses without a full wash. They'd rather just charge a little more to hire more dishwashers and be able to absolutely guarantee that there's no leftover beer/water in your glass when they refill it, and that the glass is refrigerated if that's something they want.

I've always heard the head/foam had more to do with how you pour the beer (more impact/movement = more foam), but it makes sense that temperature affects it as well. There's some kind of official course on how to pour Guinness to get the correct head on it. I don't remember the whole thing, but it was something about holding the glass the correct distance from the tap and tilting it so that the beer "slides" down the side of the glass rather than a direct perpendicular impact with the beer already in the glass (which makes more foam).

For Weizen beer, you always give the glass a quick rinse beforehand to get rid of detergent remains, so you can actually get a foam "crown" - if there is even the tiniest amount of detergent present, the foam collapses.