They are just getting more persistent, unfortunately. We had a huge uptick right before we did our software update, and then installed a new software program that scans posts by new users and sequesters new ones in a moderation queue for approval.
I probably delete 30 accounts or more a day before you even see them, thanks to that program, so, though it's cold comfort, believe me that it could be much worse!
The ones that are still making it through look a little more "normal" to the software than some of the blatant gobbledegook or foreign spam that it catches easily.
We're going to be working on increasing the difficulty/decreasing the Google-ability of our horsey registration questions when we have a minute to also help ratchet up the defenses against them.
Sorry for the inconvenience--I wish there was a easy way to make them all disappear for good!