Let us assume that you want to register for an expensive conference (e.g., SIGAda 2009). Let us say that you would like to get a discount, and decide to join the Association for Computing Machinery (ACM) despite its retro name.
In this case, and in addition to dozens of emails, you will receive a wonderful full-page color certificate and a congratulations letter for having satisfied the requirements to become a professional member of the ACM. What are those requirements? Having a credit card is apparently enough. I guess one is supposed to be proud to have joined such an elitist institution.
And by the way, do not dare put an accented character anywhere in your name or address. On postal mail, such as the issues of Communications of the ACM, “Télécom ParisTech” will be listed as “T L COM PARISTECH”. Hello ACM, this is 2009.
Edit 2010-11-01: I just received a mail with “We hope that you take pride in being a Professional Member of the world’s premier society whose mission is the advancement of computing as a science and profession”. Wow! I guess I should be proud because my institute payed my fees.