~Well, it's winter and my wiper blades now have minds of their own.
~Sometimes they work fine - usually they do not.   My front passenger
~side seems to work fine nearly all the time.  My rear wiper rarely
~works at all.  My driver side wiper usually only works on the bottom
~half.  The top half doesn't even seem to be touching the windshield.
~This makes for very dangerous driving, because I can't use washer
fluid
~when driving as it will just freeze to the windshield and the wiper
~will just breeze right over it leaving it untouched.
~
~Because the driver side and rear wipers will work fine on occasion, I
~am concerned that changing the blades will not do the trick. Any
advice
~on what may be causing this and how to fix it?
~
~Thanks in advance!

You could try bending the wiper arm a little bit, so it bows away from
the window and thereby applies a bit more force to holding the wiper
on the glass. Shouldn't be hard to try, or undo if needbe.

Yours might may be a common malady that others have resolved, but if you
decide to keep the model and year of the vehicle a secret, I don't know how
they could help you.

Barring that information:
Sounds like your driver side wiper arm is bent out of shape, has a weak
spring, or (more likely if the vehicle is old), has a worn socket. It may be
worth trying to switch them around and seeing what happens (I am assuming
that right and left are identical - may not be true in your case). If that
helps with your driver side, it's time to spend a few bucks on a new arm --
or two.
As for the rear - you just gave us no information to chew on. What does
'rarely works' mean? The motor doesn't turn? Could be anything from a burned
fuse to a bad switch, to a weak/dead motor. Does it move when you pull the
arm off the glass (making the motor load much lighter)?

The many joints in the blades are likely frozen, keeping them from flexing
to match the curve of the windshield. I usually just reach out the window
as my side goes up, lift the blade off the glass, and let it snap back down.
Or you could get some "winter blades" that are encased in rubber.

Lets face it, is it really worth all the fuss fooling with probably old
worn-old wiper blades?  Seriously, winter wiper blades are only $10-$12
each, at the most (unless you buy the more expensive Teflon coated ones) and
if you switch them in the spring with an all season blade, you'll probably
get many years of service out of one set.  I keep two sets of blades for my
vehicles, all season and winter blades, which I usually change at the same
time I switch my tires.  Do you know how old the set on your car is now?
Are they winter or summer blades (there is a difference, winter blades are
wrapped in rubber usually)?

Like someone else suggested, try bending the wiper arm as it may have lost
its spring over the years, helping to hold the blade firmly against the
glass.  Something else you can try is to take an old rag and some rubbing
alcohol and clean both sides of the rubber edge on the blade.  The rubber
tends to dry out and crack, thus giving you smears on the windshield, the
alcohol should help to keep it soft and moist.  If all else fails, throw
these ones out and pick up another pair.

You changed your summer tires to snow tires to help keep the car on the
road, now change the wiper blades so you can see where that road is.

Sharky