This Shabbos is unique in that it is the official release day of Harry Potter and the Half-Blood Prince (Book 6). This post will not deal with whether one may, in general, read Harry Potter during the week or on Shabbos. Let us assume that your rabbi is lenient and allows going to baseball games and reading Harry Potter. The question here is about the laws of Shabbos. Stores are timing the release of the book so that those who have ordered in advance will receive it in the mail (or via UPS) this Shabbos. May an observant Jewish family receive, open and read the book this Shabbos or will they have to wait until after Shabbos (and, if so, how long)?
Because there are so many opinions on this issue, everyone is advised to ask their own rabbi. In this post, I will be following the position of R. Yehoshua Neuwirth in his Shemiras Shabbos Ke-Hilkhasah (SSK).
I. Mail on Shabbos
Jews are obligated to rest from creative labor on Shabbos. Gentiles, of course, are not. Can a Jew, therefore, ask or hire a gentile to perform all of his needs for him on Shabbos, thereby circumventing the laws? No. There is a specific rabbinic prohibition against doing that-- called amirah la-nokhri--that closes the loophole (although it is left open in certain circumstances, one which we will see shortly).
Therefore, a Jew cannot give work to a gentile on Friday afternoon, e.g. giving a suit to a dry cleaner, and demand that the work be complete by Saturday night because the gentile will be forced to work on Shabbos for the Jew. However, if the Jew gives it to the gentile on Friday afternoon and demands that it be done by Monday morning, the gentile can choose when to perform the work and, if he decides to do it on Shabbos, it is his own choice and not prohibited.
Centuries ago, the question arose about the status of mail on Shabbos. Can a Jew send a letter? On the one hand, the postal worker is delivering the Jew's letter on Shabbos. On the other, the Jew does not care whether it is delivered on that day or a later day. The consensus is that regular mail is allowed to be sent (unless the postal service is staffed largely by Jews, as was the case a few decades ago in NY and is currently in Israel) but any mail that is sent to be delivered specifically on Shabbos, i.e. express or overnight mail, is not allowed (SSK 31:20).
Similarly, mail that arrives on Shabbos is not considered as if a prohibition was performed on it and is not, therefore, inherently forbidden for use on that Shabbos (SSK 31:22). This is so even if the package was brought through a place that has no eruv [such as Flatbush ;) ] or from outside of one's tehum Shabbos boundary (SSK 31:23).
II. Opening a Package on Shabbos
The Mishnah Berurah (340:41) generally prohibits opening letters (and, by implication, packages) on Shabbos because the containers are reusable. The SSK (28:4) quotes this ruling in the text, but in footnote 15 quotes R. Shlomo Zalman Auerbach as questioning the reason for this prohibition, since the envelope is generally disposed and not reused. If one intentionally opens the package in such a way that the box is no longer usable and must be thrown out, this should be entirely permissible. This is also the position of the Hazon Ish and R. Shlomo Fisher (cited in Piskei Teshuvos 340:29). (Assuming, of course, that the letter or package contains no muktzeh information, such as financial statements or bills.)
However, even the Mishnah Berurah agrees that one may tell a gentile, such as a nice neighbor or a random passerby, that one may not open the box because it is Shabbos. This should be enough of a hint that the gentile will open the box for you. This is allowed despite the general prohibition of amirah la-nokhri mentioned above (SSK 31:22).
III. Harry Potter on Shabbos
Given all the above, may one open up the Harry Potter package delivered this Shabbos? Let me quote from the official English translation of SSK, Shemirath Shabbath: A Guide to the Practical Observance of Shabbath (31:23, p. 495):
a. One may use on Shabbath the contents of a parcel delivered that day by a non-Jewish mailman.In my estimation, the bookstores are very particular that this book be delivered on Saturday, July 16. I suspect that if many people do not receive their books on this day, there is going to be a big stink and someone somewhere is going to be fired.
b. This is so provided that the sender was not particular that the parcel should be delivered on Shabbath.
UPDATE: See this post.