Re: how strong is the magnetic pull of the earth?

The Earths magnetic is about 30 microTesla strong (Tesla is a unit with 
which to measure the strength of magnetic fields, and is equal to 1 Newton 
per meter-Amphere).  

I said the field is "about" 30 microTesla, because it is changing 
(decreasing) at about 6-8%/year, and because it varies slightly depending 
on where on Earth you happen to be.  

As far as the weight it can pull...not sure where you're going with this 
one, but a magnet can't "pull" anything unless it's either ionized or 
polarized (two ways of saying the same thing).  Let's just say that, if 
you hold a largish strong magnet in your hand (rare-earth magnets are good 
for this, because they're strong magnets for their weight), you can feel 
the tug of the Earths field if you quickly swing it around (from north to 
south, for example).  The magnetic field of the Earth also "pulls" 
(accelerates) electrons and protons, which is what gives us the Northern 
Lights (aurora borealis). 

For more info about the Earth's magnetic field, a URL that I highly 
recommend follows: http://www-spof.gsfc.nasa.gov/Education/Intro.html

and another is: http://dac3.pfrr.alaska.edu/aurora/

Lots of links from these pages will take you to just about anything you 
might want to know about Earths magnetic field.