One of the things that was something of a surprise -- and a challenge -- to us was finding out which walls in our house were bearing walls. Since we wanted to make rather large holes in various walls to create a more open floor plan on the first floor, we need to know which walls might make the house fall down if we touched them. Pretty sensible of us, I think. Anyway, normally the easiest way to tell which is a bearing wall if you've got a little access to the innards of your house is to see which way the floor joists run. The bearing walls will be the ones which are perpendicular to the floor and ceiling joists (if I were better at physics and spatial relationships I'd be able to explain why this is true to you, but I'm not, so I'm just telling you what I know [somebody who is smarter than me will undoubtedly weigh in in the comments, keep an eye out]).
Anyway, so when we first pulled down the plaster in the dining room and family room, last May, we were surprised and a little dismayed to find that our handy little tip didn't work. See, the floor joists on the first floor run in the complete opposite direction of the floor joists on the second floor. Which is not supposed to happen. I mean, it's not like a horrible disaster which might cause the house to come crashing down around our ears or anything, but it's not really normal, either. And of course it made it awfully confusing trying to figure out which walls were load bearing.
As it turns out, all of the walls in the dining room are load bearing. So it didn't really matter anyway.
Anyway, now that the floors and ceilings and walls and stuff are all gone, I thought I'd try to get a photo of this little architectural phenomenon for you.
Somewhere to the left of the photo frame, the floor joists on the first floor actually somehow change direction. Like it's okay to do that or something. Not okay, floor! Not okay!