They reported in a new blog post yesterday that they had reached new milestones, exceeded expectation, and all that stuff.
Their subscriber count is up (there's no mention of how many users have subscribed, though). Scribd is also reporting that their catalog has reached over 100,000 titles from 900+ publishers, and that users have added over 1 million ebooks to their reading lists, a sign they're planning to read the books at some point.
Scribd's success is probably due to their wide availability (global) and the large size of their catalog at launch. Of the 6 competing services in the US, this was the one service that was available on the most platform (Android, iOS, web browser) and with the most books.
While the Kindle Owner's lending Library probably has more titles (and more users), it is limited to only working on Kindle hardware. Oyster is still only available on the iPad and iPhone, and while 24Symbols does have apps on multiple platforms they still do not have a large selection of titles (more details here).