Some are, some are not -- at least in Norway. Unions are particularly strong in the government sector, and generally even developers will be unionised there -- in the private sector there's a general feel that a software engineer is in such a strong position that they don't need a union.

Like for most types of work -- that's probably wrong. But people only ever figure it out when it's too late.

At my previous workplace (a research institute) I believe pretty much 100% were organized, both researchers, developers, sys.admins and other staff.