Back in 2000/2001 I worked for an Irish broadcaster on their online presence. The company was heavily unionised. Because they weren't sure which union us techies should be in, the local chapter of the National Union of Journalists (NUJ) decide that we belonged under them.
Their reasoning was that they had technical print workers part and the Internet was a form of electric printing. Few of us joined.
And when a inevitable round of lay-offs came the union members got better severance packages. In a heavily unionised environment it's definitely worth the membership dues.
If you think it's absurd for a programmers union what do you think of an employer's union? http://www.ibec.ie/ has always been called, and behaved as, the employers union despite dropping union from their name in 1990.