I just wanted to post a good experience (if I can call it that)

Last year, my jetta would start on cold days without being plugged in
(-15 Celsius was about as cold as it got in Kingston when unplugged).
It would turn over slow, but eventually it would go.

This year, no such luck.  I had problems when it was -10 C.  I often
needed a boost after work, which was kind of embarrassing (my battery
would only crank for 30 seconds).  I was hoping to squeeze through the
rest of this winter, but after enough embarrassment, I bought a new
battery.  I bought a 'Motomaster 72' battery from Canadian Tire.  It
was their last one (manufactured Oct 2005), and I was skeptical to
take it; but I was in a bind, so I did.  The clerk was a real piece of
work.  I asked him if it was good, and he took the voltage across the
battery.  11.98 V.  That doesn't mean a whole lot...

Because, when I got stuck the next day, and tried to boost my dead
battery off the 'new' battery, I wouldn't even get a spark off the
cables (and a very weak spark from shorting the cables for a split
second).  The Queen's University parking attendant tried to help me
out, and offered me a boost.  It was about -25 C.  We tried for about
1/2 an hour, letting the battery charge for 5 - 10 minutes each time.
Nothing.  Just cranking.

The parking attendant was kind enough not to give me a ticket on my
illegally parked car for the day.  I tried getting a boost when it was
only -20 C that day.  Again nothing.

I took the 'new' battery in, charged it up, and started it on the next
-13 C day.  It cranked for a long time before firing, and after
firing, took another 10 seconds to get up to running speed.

I guess only about 1 or 2 of my glow plugs were working.

At work the next day, I plugged it in (-25 C).  Didn't matter -- STILL
wouldn't start.  I was steaming mad.  I took the bus home and picked
up 4 new Bosch glow plugs ($20 /each at canadian tire) on the way in
the next day.  Tried to change them myself at lunch (I only have a few
wrenches...).  I got one done (approximately 1 hour), and that was a
hassle and a half at -25 C (the terminal broke off one, and I had to
clamp a vice grip on it to wrench off the rusty nut).  I didn't have
another 4 hours to finish, and the one I changed was the easiest to
access on the driver's side (so I wasn't looking forward to the other
3).  The one plug was enough to start it though (painfully - cranked
for about 30 seconds, and I had to push the choke in).  I brought it
to the mechanic, and they did it in about 1 hour for $70.  Not bad.

I should have done that long ago, when the problem started.

Now, my car fires before you even hear a full crank at -15 to -20 C
without being plugged in.  It's amazing...

-Randy