Oyster is an all-you-can-read ebook subscription program. Commonly described as Netflix-for-Books. Officially it was opened up in September, but it is still in a private testing phase. I signed up and have used it for the last three weeks. 
My overall impression is fairly positive. When you sign up you are asked to choose five books from your computer browser. These five books will be in your account to get started. The main problem is that on the computer, there is not a search function. So you have to look through book covers sorted into categories. These are their most popular books, so you should not have too much problem finding books you are interested it.
Once you complete the registration process (pretty basic) and give your credit card information ($9.95 a month but with a free one month trial) you are emailed a link for the iPhone app (you can just find it in the app store as well). Once you sign into the app on your iPhone, you can search for books, load the books that you chose on your computer, and update your profile (connect to Facebook or Twitter, search for friends that are on Oyster, list your favorite books, add a picture and write a bio).
Oyster has a good selection of books, they claim 100,000 books, but Smashwords has also said that their entire 250,000 book catalogue of independent authors will be added soon. I was able to find CS Lewis, Ursula Le Guin, NT Wright, Margaret Atwood, Susan Howatch and a lot of other books that I actually want to read.
I put about a dozen books on my initial to read list. These are back-list books, books that are a year or so old, so don’t expect anything that is on the current best seller list. But there are a number of books that were on a best seller list in the past.
The first time you access a book it has to download to the iPhone. So you need web access for that. But once it is downloaded you can read anywhere without needing access the internet. According to the FAQ page, the 10 most recently read books are stored on the phone.
The settings are fairly simple. You can change the background and font colors, the brightness of the screen and the size of the font. There are 5 preset background and font combinations, 3 are various white background and different black fonts, one is a tan-ish background with black font and the final is a black background with a white font. There are also five font sizes that range from about 25 characters across the screen to about 45 characters across the screen.
The app is limited to portrait mode only, but this is probably best for reading.
Oyster would also benefit from connection to GoodReads.com or another social media Book discovery service. You can follow other users and see what they are using, but unsurprisingly no one from my Facebook, Twitter or phone contacts have signed up with Oyster thus far. You can mark books as read and choose your favorite books (but only books that currently are in Oyster.) I listened to an interview with the CEO of Oyster Books and there are plans for good social features for Oyster, but at least right now I don’t have anyone to be social with on Oyster.
Overall Oyster seems like a good system. And for someone like myself that reads a lot it could save money. But it is a subscription model, you are not buying books, you are buying temporary access to books. So if keeping the books is important to you, then this might not be a model for you. And if you read a lot of particular type of book or have particular authors that you love, at least for now, Oyster may not have those books. I looked at my currently reading list and none of those 9 books were on Oyster. That being said, there were plenty of books that I was interested in reading, just not all of the book I am interested in reading.
The biggest problem for me is that it is only available on the iPhone. According to twitter, an iPad version should be available this fall (now available) and Oyster would like to expand to other platforms as well. When I was younger and my ebook options were fewer (and my eyes were better) I read a lot on a Palm IIIx and then on a Dell Axim PDA. But once I picked up my first eInk reader, I have not looked back. eInk is a superior screen technology that is much better for your eyes and much more comfortable to read. But Amazon is not going to allow Oyster to access the kindle. Theoretically, Oyster could work on an epub version that would work on a Nook, Kobo or Sony eInk reader, but that is a long way off. If there were an eInk option today, I would have no real complaints.
If you are interested request an invitation (seems to be giving out invitations fairly quickly.)
After using it for three weeks, I personally cannot justify keeping the subscription. I just do not read on my iphone enough. I prefer reading on my kindle. And I have such a large number of books already purchased that the unlimited discovery of new books is not enough to keep me in the system. However, you are interested in reading on an iphone (or ipad) and read at least two books a month, then this is a good system.
I will take the Oyster subscription if it is still available.
I sent it to you.