That's a hard question to answer because it varies so much. I haven't been on Hub pages long myself, but I became a writer before the web content explosion so I started doing this more for fun (to write about what I want to write about, not what my clients want me to write about) than for profit.
From a single article, a realistic expectation is maybe a few bucks over the next few years. That would be average or a little above average for most of these types of content venues. Some people hit on a timely topic and can get lucky and make more, but this is rare. Most will make even less-- especially if you don't have many hubs or give up after a few weeks/months.
Writing web content for these kinds of websites is not an easy way to make money; especially now. A few years ago it was a little easier, but now the internet is flooded with this kinds of content now. If someone is really good and really diligent (adding new great content, daily/weekly, for months/years, preferably on more than one website) they may make some nice pocket money. Few people will make a living writing web content for (pardon the expression) 'content mills' anymore, no matter how they try. It helps if they have a niche and get some good ad affiliates, and it helps to have serious talents or expertise in an area, but if you're that good and getting that many readers you'd do better to move your writing to your own website.
In my experience, when it comes to ad rev. web content sites (Hubpages, Associated Content, Squidoo, etc.) most people will get frustrated after a few weeks/months and give up and never earn anything besides pocket change; these are usually people who were never really serious about writing, they just wanted what they thought would be easy income from home. Some will make some money-- maybe $25, $50 or even as much as a couple hundred per month-- but even to earn this much usually requires putting in a lot of hours. Very few will reach the heights of earning even a modest full time income from web content writing for ad revenue, and they usually have well above average talent or a highly sought expertise along with good writing skills. Others move on to a freelance business finding clients or writing for paying venues if they're really interested in a writing career, giving up ad revenue web content or doing it for a little extra pocket money.