Approximately how many domain names have been registered for each of
the extensions listed.  What percentage of domain names registered
will resolve to an internet site?  What percentage of these sites does
Google cache?
.com .net .us .biz .info .tv .org .ws .cc .bz

Hi n2film-ga!
I have found info on some of the extensions you have listed.

Total number of gTLD domains registered worldwide (14 April 2002)
com  21.581.810
net   3.710.409
org   2.372.801
biz     624.743
info    791.551
Source: Zooknic http://www.zooknic.com/ (where you can find many other
statistics!)

Total domains registered worldwide: 30.696.524 (Source:
DomainStats.com http://www.domainstats.com/)

I hope this will help you!

Best Regards
mdb-ga

oh! 
You can find more info with this search:

Google - number domains registered statistics +com +org +edu +net
://www.google.com/search?q=number+domains+registered+statistics+%2Bcom+%2Borg+%2Bedu+%2Bnet&hl=en&lr=&start=0&sa=N

;-)

"What percentage of domain names registered will resolve to an
internet site?"

I don't think there have been any studies on that.  It would be very
hard to technically do an accurate survey.  Unless someone posts
otherwise, it would be my suggestion that you remove that request from
your question and just go with the other two questions.  Thanks!

xemion-ga

One might be able to use NetCraft data to answer the question "What
percentage of domain names registered will resolve to an internet
site?"

see: http://www.netcraft.com/survey/Reports/200205/bydomain/index.html

http://www.isc.org/ds/
is from the people that author THE DEFINITIVE DNS software and their
domain survey does some kind of check to see if the address responds
before including it in the survey. You might find the data useful.