I've got 4 signups so far. I think it takes a bit of luck, but you also have to get into the habit of using referral trackers for every link to your hubs or others. I post links to my hubs on several social media websites which is where I think I have gotten most of the signups.
You can always email friends or relatives with a link and encourage them to signup!
Bottom line, it just takes consistency. Make sure any links in your hubs also have referral trackers, even when going to other hubbers hubs!