But there fast approaches a point in time for every new company where you just aren't that new anymore, and knocking on the same doors with the same tired song and dance will get you nowhere. You talked a lot of smack as a new start-up (to garner attention), and now it's time to back it up.
Specifically, you need to show that you're: (1) moving the needle with the product, and (2) generating momentum with customers.
For the vast majority of start-ups, this is where the transmission falls out of the PR machine.
For a lot of vendors (whose original vision for their product was compelling), the new features / versions of the product are released in a very ad hoc, non sequitur fashion. There is a real lack of discipline in creating some sort of compelling progression that both resonates with the target customer and demonstrates to target journalists and analysts that the original vision is being fulfilled (and new opportunities are being exploited).
And most vendors are horrible at telling their product / service momentum story through the voice of their customers. Sometimes it's because one or more of their marquee customers have a strict policy against participating in PR. Other times it's simply because the company isn't paying enough attention to capture the good customer stories. But most often, I would chalk it up to vendors simply not putting in place the infrastructure from day one to capture public customer references.
Proving momentum (both on the product evolution, and customer adoption) is often a plodding exercise. You can't just drum it up overnight. The key (for early stage ventures) is to have a systematic approach to both of these key traction points from day one -- rather than snatching and grabbing when the PR drought hits.