Copia failed in part because they couldn't find a good enough reason for readers to join Copia's walled garden instead of doing their social reading on the many other social reading sites. BookShout might have suffered the same fate, but I think they found a great reason to join.
Like many readers, I have ebooks spread across so many stores that I have TBH lost track. That's part of the reason why I believe in stripping DRM so I can manage all my ebooks locally; it's a far smaller headache. But now BookShout offers an alternative that will appeal to some.
They will let you import your ebooks.
Right now you can only import ebooks from B&N and Amazon, but according to the press release 5 of the 6 major US publishers have signed up to allow this service. It took me a couple tries but it does indeed work like promised.
This feature is only available via the iPad app, not the website, but it does let you import your ebooks. I have just read a couple of my Kindle ebooks inside the BookShout app and I am surprised that it worked.
Great feature, isn't it? I wouldn't get too attached; this kind of thing depends on the goodwill of Amazon, B&N, and publishers. If someone gets unhappy with the service they will take steps to crush it (or buy it, in the case of Amazon). Remember Findings, the web clippings service which lost their Kindle privileges? BookShout has much the same access, and they could lose their privileges as well.
But that shouldn't dull your enjoyment; this is a cool feature.