The % of Employed Wage & Salary Workers who are union members is down from 20.1% in 1983 to 12% in 2006. 2005 was 12.5%. Gov't sector workers have 36% union membership while the Private sector has only 7%; within these groups, Local Gov't is even higher, at 42% (this would include teachers, police, firefighters, etc.), while in the Private Sector, the Financial Activities subgroup has the lowest union membership rate (1.9%).
5 states have less than 5% union membership: N.C., S.C., Virginia, Georgia, and Texas.
4 states have greater than 20% union membership, with Hawaii topping the list at just under 25%: Hawaii, NY, Alaska, and NJ.
Why does this matter? Unions are very influential in elections in terms of financial support to campaigns, but in terms of voters, 1 out of 8 isn't that impressive. The 2008 election promises to have no shortage of warchest funds for the candidates, so it would look to me like there won't be quite the level of catering to labor unions that there has been in the past.