Related to but different from this question, I have two three-way switches in my house, which are in multi-gang boxes at the top and bottom of the staircase and control lights at the top and bottom landings. I know for a fact, having fixed the "hot" side of the wiring to the three-way switches before, that the switches (along with others in both boxes) are fed by different circuits. However, all of the white neutrals in each box are twisted together into one bundle and wire-nutted; this predates any work I did on the circuit, but I don't know if this is the work of the original electrician or the "handyman" whose work I've been fixing since I moved in.
As these joined neutrals include the travelers of both three-way circuits, the neutrals from the nearest light to each box, and the neutral heading back to the panel from each box, these two circuits' neutrals have multiple junction points that tie the neutrals together.
Is this dangerous (from a fire hazard perspective)? My Google-fu brought up some similar questions, but the answers were all along the lines of answers to the related question in the link: "a shared neutral is bad". However, this isn't a "shared neutral" as in one white wire carrying the load from two circuits; this is two white wires carrying the load from two circuits, but the two white wires are both carrying the load from either circuit. So, to my way of thinking, there's plenty of copper to get the power back to the panel without overheating. And obviously there are no AFCI/GFCI breakers in the house (plenty of GFCI receptacles), because everything on both circuits works fine (they'd trip as soon as I turned a light on otherwise). The only concern AFAIK would be shock safety, as you'd basically have to make sure both of the breakers were off before working in either switch box (something I would do anyway; I wouldn't want ANYTHING hot in either box if I were messing with these switches, regardless of whether the neutrals are separate or not).
EDIT: picture == word*1000: