I am looking for trend data from 2-3 reliable sources
(Gartner/Meta/etc) on the accumulation of digital media such as mp3s
on users' home hard drives.  Ideally this would include the past five
years and projections for the next five years.  The data would answer
questions such as how many broadband home Internet users are
accumulating digital media and what is the total data volume in
gigabytes?

Check out emarketer.com which has quite a bit of informationm.  Most
of thier data is subscription based, but there is some good
information at no cost as well.

For example:
Crossing the digital Divide -- focus on African American user, but
counts all dempgraphic is broadband usage:
http://www.emarketer.com/Article.aspx?1003658

Also, I found a interesting site called Trendwatching.com.  It make
for some interesting reading.  I am continuely surprised how the
information I see in here dove tails with business book and articles I
am reading.  The only thing it TrendWatching.com lack (sometimes) is
the hardcore numbers.

Hope you find this useful.

Alex In NYC (negentropy.blogspot.com)