F+W Media and Sourcebooks are both starting e-book subscription sites. F+W is focusing on specialty titles--you get unlimited access in return for a hefty ($199 per year) fee, so it's basically like a paid research library. Sourcebooks is focusing on romance novels, and it's much cheaper ($9.99 for six months), but the number of titles you can access is quite limited--it's more like a book club, with a discount program thrown in.
Both services rely on curation to appeal to readers. F+W is appealing to a fairly thin slice of deep-pocked institutions and businesses that feel they must have access to these books. Sourcebooks is appealing to fans of its writers.
Whether these services are going to work or not, I don't know--that's going to depend on whether or not enough people think they provide a good value. But they are both examples of the experimentation going on with online e-book retail.
More details on the Sourcebooks service can be found here.