"Successful" is a relative concept. I think 1,000+ views a month is definitely successful, whereas 500+ views is moderately successful. I've only been here a couple months, and so far I've only got one hub that fits that "moderately successful category." It's about persuasive writing prompts for use in English classes.
I have a few other hubs that are at or near the 100+ views/month category. I wouldn't say these are extremely successful, but as they age and/or receive some backlinks, they could potentially get more traffic. These are mostly about the House of Cards series on Netflix.
I've written a lot more on Yahoo! Voices, and I find that about 10% of my articles are really successful, another handful are minor successes, and a lot are flops. This matches up with statistics I read from a niche-site creator, who suggested that about 10 to 20% of his sites were big earners, 20 to 30% were low earners, and the rest (half or more) were basically flops.