Is it worth serving on a program committee if you are going into industry? I got invited to be on the poster track program committee for a CS conference.  Is it worth accepting the invitation if I am going to become a software engineer when I graduate?

Also, if I review the posters, should I put it on my resume?  (I reviewed posters last year and didn't put it on my resume, but maybe I should.)
You might address this as a 'return on investment' type of problem.

Your investment: you will need to put in some time in reviewing the articles, writing down your findings, perhaps communicating with the rest of the programming committee, etc. How you value this investment depends largely on how much time you have available, how much you enjoy (or dislike) reading the articles on this particular topic, how experienced you are in reviewing, etc.

Return: you might learn something from reading the articles, you might feel that it is benevolent to contribute to science, and it might be relevant for your CV. Again, the value of these depends on your particular situation. Is the conference topic relevant for your career? Do future employers care about these type of activities? Do you care about contributing to science?

The value of the different elements will vary for everybody (depending on their personality and situation), so it is impossible to provide a generic answer.