I've installed an extension to allow deleting users... as you may have noticed on the Recent Changes page. Sorry about the noise there, as I work though getting rid of more, I'll use my bot account to keep the noise down.
Admins can access it at Special:UserMerge. Before a user is deleted, all of its history needs to be transfered to another user (hence the "Merge" part of the name). There are a couple of spam testing accounts around that you can use (Aeakett-spamtest1 for example).
I'm heading to bed for the evening, but will continue to prune bogus accounts tomorrow. If anybody is interested in in helping, just providing a list of bogus usernames would be a great help (I have a semi-automatic workflow to ease the pain of deleting batches of accounts and a raw list of accounts is the starting point).
Marvellous - excellent news Aeakett - thanks for this. One needs to be a bureaucrat to do this though and I am not one (well on this wiki anyway).
OK, I've got my bot deleting 1000+ accounts that have signed up since last November and have zero edits. I've probably missed a few, and it's possible that there are a couple of false positives that will get blown away, but given the volume I'm going to say that this is an acceptable loss. I've also fixed it so that admins and not just bureaucrats can merge/delete users (I missed that step in the setup in my initial excitement).
Also, while I was poking around I saw some extensions that might help out in the realm of bogus sign-ups. If one of them fits the bill, it will probably be way easier to implement it than my current plan to write a whole new extension. I'll be looking into them this weekend.