Google earth is a great tool... but I prefer another method to
visualize airspace boundries. You can download 3-D representations of
restricted airspace from:
http://www.lloydbailey.net/airspace.html
The website is slightly funky... click on the red "plus" sign next to
"DAFIF 3-D Airspace", then pick your country and state. Yep,
restricted airspace for the entire world is available for the next
time you are flying in Afghanistan.

I find this to be a VERY helpful way to orient yourself to airspace
size, shape and boundries. The airspace cylinders are superimposed
over the satellite images from Google, so you can see relevant
landmarks as they appear from the air. I prefer reading the sectional
on paper. Seeing the "upside down wedding cake" of the class C
airspace is helpful. You can even position your Google Earth "camera"
so you can fly UNDER the floor of the outer cylinder and get a great
feeling for where the airspace extends to. If you really wanted to...
you could show both the 3D outlines of the airspace along with the
sectionals too.

You may want to selectively turn OFF some of the airspace designations
(like class E) using the checkboxes under the "places" tab on the
lefthand side of Google Earth. This will declutter the image so you
can see what you are interested in.

I've got a pic online showing my tracing on a recent flight when I
briefly flew over the Class D of our neighboring airport. (Yep, I was
in contact with them via radio)
http://www.flickr.com/photos/55092851@N00/502828393/

Enjoy!
Jim
(Remove nospam from my email if you want to reach me)