I joined this site because I was curious about what it is. I requested an invite and was accepted a few days later - I think it depends on whether or not your email is associated with social media accounts. I've never been one to not be blunt so I'll be blunt: it's a product pushing site disguised as a rewards community type of thing where your "popularity" and activity earns you better rewards. When you join, they assess your "influence" by your facebook, if you have a blog, twitter, youtube, etc. You get assigned a number and depending on that number you may qualify for "vox boxes," - sounds fun right? You get to try random products depending on the category which you can sign up to be an expert of - beauty, exercise, geek stuff, etc.
However, I think Influenster is less about trending and more about product pushing and brand marketing. By offering free stuff for their users, they ensure that bloggers and vloggers promote items like gel shoe inserts, hair ties (which I actually want to try) and toothpaste to their audiences. In essence, instead of marketing teams trying to find individuals to try and promote items - Influenster aggregates individuals on behalf of them and then the brands that are featured on Influenster let Influenster handle the distribution and representation. So who's really influencing whom? It's definitely less the users and more so the brands involved. Going back to the dSLR example, for people who've never been exposed to a dSLR - they might see the Canon rebel, look at the reviews and go out to buy one. Sure, google exists for the more knowledgeable buyer but for the people that don't want to wade through long product reviews and spec ratings - Influenster just might influence them with their selective branding.
You cannot add products or labels to their database to review (reviewing earns you more cred with your expert category and ups your overall score - giving you a better chance at being selected for a vox box). This is proof that it's really more about a pre-selected group of item (buy Xbox not PS, buy Canon not Nikon) and social media slowly trickling those brands to consumers. The only influence anyone has is what Influenster tells them to have - any indie, niche or non corporate labels/entities anyone has an interest in does not exist. That being said, if you love KRAFT MAC AND CHEESE, Neutrogena and Taco Bell you can review them to your heart's content (even shady one liners like "Great") and for your hard work, might as well get free samples.