Is this really that bad?

The rating isn't unreliable, as long as you understand what the rating actually reflects. It's not an indicator of a film's technical or artistic merits so much as it is a simple estimation of its popularity among IMDB users who have taken the time to register with the site and cast their votes. If we dissected these votes deeply enough we'd probably find that a good deal of IMDB voters tend to spend more time rating the films they either loved or hated than they do those films that struck them as so-so. And then there are also those in that unique segment, as you pointed out, that rate not on the experience of viewing, but on their desire to see, or disgust at the thought of seeing, the film in question.

Statistically speaking, that's a narrow sample and would likely prove rather skewed when set against a true random sampling of the public, though in most cases you could reasonably infer that a film popular on IMDB is similarly popular in the "outside world." Obviously, a person's subjective judgment of a film's technical and artistic merits usually plays a a key role in informing the individual's opinion of the film, and so these aspects can't be totally divorced from whatever defines "popularity" here--but rather than thinking of IMBD's star-rating system as a measure of a film's subjective quality, you'd be better served to think of it as an objective measure of what percentage (roughly analogous to the star rating multiplied by 10) of IMDB users the film appeals to. Highly-rated, "popular" movies like those on the Top 250 will generally reach across many demographics, while middle-rated movies find their appeal in smaller niches and the cult-mentality (which sometimes is popularity by means of unpopularity).

Low-rated movies like the Biebs here geared to highly-specific demographics with a particular interest in the film's subject matter--in this case, I suspect, mainly frivolous tween girls of affluent families. And so in this sense, the IMDB ratings provide a somewhat valuable insight. If you were one such tween girl with the hots for Biebs who also subscribed to the ideas in my minor dissertation on the IMDB rating system, and came to IMDB to see how "popular" JB:NSN was at the moment, I could infer from the 1.1 rating that this movie was made specifically for me and people like me, a tween girl with the hots for the Biebs with lots of mommy and daddy's money to spend on movies and concerts and posters, and that I should probably go see this movie and buy ten copies when it comes to Blu Ray. Most of the rest of us could as easily conclude that this probably hasn't anything to offer us, unless we happen to be a parent of the aforementioned tween.