I've joined!! But not using my real name OR work name, as some people who are very against us and the idea of our having a union cannot be relied upon not to use dirty tricks against our members. I know a few people who are members and have done this as well.
I am really happy I have joined, apart from the feeling of being connected and having that extra support, I also like feeling I have some direction to get involved as an activist (And beyond that your union card gets you some lovely perks).