What percentage of the population in the US wears a wristwatch?

Here's a January 2005 article from a university newspaper on the
decline of wristwatch popularity.  The article suggests a
wristwatch-wearing rate of 8-10% among students observed in classes at
Portland State University.
http://www.dailyvanguard.com/vnews/display.v/ART/2005/01/13/41e63d6aa687d


Unfortunately, most of the other information available relates to
wristwatch production, not wristwatch-wearing, though presumably there
is a correlation.

This document, a business school case study of the evolution of the
watch industry, is an outstanding resource on watch production.  For
instance, it reveals that 1.245 million watches (it actually says
billion, but this appears to be a misprint after checking the source
of the data)  were produced in 2002, 60% of which came from Japan.
http://www.thunderbird.edu/pdf/about_us/case_series/a07040003.pdf

This website, by the Japan Clock & Watch Association, has lots of
figures on watch production (you can select years 1999-2003):
http://www.jcwa.or.jp/eng/syou_03.html

This page appears to have the most recent production numbers (2003),
indicating a 4% increase in production from 2002:
http://www.jcwa.or.jp/eng/syou_03c.html

This entry in Wikipedia for Timex states that they have sold over 500
million watches: http://en.wikipedia.org/wiki/Timex_Corporation
However, information on the company's timeline indicates that was the
number of watches they had sold by the mid-1970s:
http://www.timex.com/150/index.html

An International Herald Tribune article from Oct. 13, 2000
("Watchmakers Say It's Time to Get Two-Faced", Thomas Crampton)
provides some information on the number of wristwatches produced
annually: "Of the 700 million watches sold around the world each year,
Hong Kong says, 650 million are produced by companies based in the
territory, many of which have factories across the border in China." 
(These numbers appear to conflict with the number cited above, though
perhaps there was a large surge in production between 2000 and 2002.)

This website, made by a wristwatch component producer, contains some
information on wristwatch production trends in Japan:
http://www.citizen.co.jp/english/release/00/00wldqty/prod2000.htm
A PDF of a similar report is available here:
http://www.citizen.co.jp/english/release/01/03kisya/pdf/0103k02.pdf


Further resources:

Academic journal article on correlation of scores on psychological
tests and watch-wearing:
http://www.buffalostate.edu/orgs/cbir/cbir-r2.asp?rec=30570

The opinion essay at the bottom of this page describes the
characteristics of watch-wearers:
http://www.wow-schools.net/reader/toccc.html

Wristwatches in movies:
http://home.xnet.com/~cmaddox/moviewatch1.html

If you're interested in wristwatches, you might also find these
articles/websites interesting:
http://www.qualitytyme.net/pages/rolex_articles/history_of_wristwatch.html
http://www.forbes.com/2003/12/03/cx_ns_1203guide_print.html
http://chronocentric.com/
http://en.wikipedia.org/wiki/Watch
http://www.compuwatch.net/

Prof. Robert Levine of UC-Santa Cruz (and others) did a study on the
speed of life in 36 US cities that appears relevant to your questions.
 He originally published the results in a journal article entitled
"The Type A city: coronary heart disease and the pace of life" (J
Behav Med. 1989 Dec;12(6):509-24).  He also published the city
rankings in a book, "A Geography of Time" (1998).  One of the criteria
in the study was the percentage of people in the downtown area who
wore wristwatches.

The top 5 cities for wristwatch-wearing were:
1. New York, NY
2. Boston, MA (tie)
2. Detroit, MI (tie)
4. Buffalo, NY
5. San Francisco, NY

The bottom 5 cities for wristwatch-wearing were:
32. Kansas City, MO
33. Nashville, TN
34. East Lansing, MI (tie)
34. Memphis, TN (tie)
36. Atlanta, GA

Unfortunately, I am not able to find the actual percentage data. 
However, I am working on that.

I have been able to find that San Jose, which placed 22nd in
wristwatch-wearers, had a watch-wearing rate of 68.5% in the downtown
area, according to a piece that aired on Minnesota Public Radio's
Marketplace program on June 28. 2001.