Couldn't really see what's the point here. my experience in academia (anecdotal) suggests that Mendeley already has a pretty substantial lead
1. we want to change the current peer review system, instead of letting 2 or 3 reviewers deciding your paper's fate, why not take advantage of ALL peers in your field? We're not quite there yet as it is a big goal, and we believe this is the right direction to head to.
2. academic journal publications are growing exponentially, how to select good papers from noise? PubUp provides peer curated selection of papers that are worth reading.
I'm completely open to an alternative service (or even a complementary one). So... I guess what I'm trying to say: Give me, one of your intended customers, a compelling use scenario or value-add proposition that might compel me to switch.
PubUp, in contrast, looks like it is designed specifically for those two things.
Presumably to use PubUp I don't need to store my PDFs in Mendeley, to have signed up to their web component, to have found a group of people whose opinions I trust, yadda yadda.
On a tangent Mendeley also certainly hasn't sewn up the market: the majority of researchers still use one of a couple of older, more established desktop apps for their reference management. That's certainly not to say that it's not a good product, it is, or that they won't become an incumbent eventually, I reckon they probably will. It's just that scientists are a notoriously hard bunch of people to reach.