Given that what you have are just hairline
cracks, my first guess is that your house is
probably in excellent shape. But check out
your doors first. Do they rub and stick
anywhere, particularly at the top or bottom?
Likewise for windows. Look to see if the
doors have been planed to fit again and again
-- if not, rejoice. Check the door jambs
with a framing square to see if they're true.
Inventory where your cracks are. For
instance, suppose you find that all those 45
degree cracks are near the east end of east -
west walls, and that the low end of the crack
is always to the west. That would indicate
that the east side of the building has gone
down a little. If there's no particular
pattern or consistency to the location and
direction of the cracks, then you just have
normal settling for a building that age, and
probably less than most houses that old.

-- J.S.