(This is an informative article about the sources of the practice of staying up all night, especially on the first night of Shavuot, to study Torah.)
All-Night Shavuos Learning: What to Learn? And Its Controversy
Rabbi Yair Hoffman 
It is a custom whose roots reach back to the earliest era of our nationhood.
To make up for the fact that our ancestors actually had slept the night of the Sinaitic revelation, religious Jews stay up all night and study Torah (Midrash Shir HaShirim Rabbah 1:56). The custom does not fault our ancestors for being ill-prepared, for how does one prepare for something that one does not know anything about? Rather, it is a custom that allows Klal Yisroel to shine ever further.
The practice is mentioned in the Zohar (Parshas Emor 98a). There it even describes the reward that awaits one who studies Torah all night. The all-night learner receives no less than seventy divine blessings from above and is crowned with a special celestial crown of the upper heavens. Then they are inscribed in a special Sefer HaZikaron.
The Arizal writes in Shaar HaKavanos that whoever stays up all night learning is assured that he will certainly live out the year. (This seems to be true under all conditions, Swine Flu or no Swine Flu.) The Chofetz Chaim records this statement lehalacha (Mishna Brurah 494:1).
There is another interesting point too. Rav Dessler zatzal writes in Michtav M’Eliyahu that time is not a straight continuum. Rather, the nature of time is like a carousel that turns in circles. He writes that each Yom Tov is actually the very same Yom Tov that Klal Yisroel experienced in thousands of years ago in the year 2448. Each day on this carousel of time has its own special unique aspect to it. With this thought of Rav Dessler in mind, let us examine the words found in the Siddur Etz Chaim (page 46a). There it states that fulfilling this practice of learning all night makes it as if we ourselves received the Torah when we hear the Krias HaTorah of Shavuos. It is therefore, as if we were actually there at Har Sinai on the actual day of Matan Torah itself!
The question is, however, what should one learn? There is a special Tikkun Lail Shavuos that much of Klal Yisroel studies each Shavuos night. It encompasses Torah, Neviim, Ksuvim, Midrashim, and certain mystical parts of Torah. The Tikkun was established by the AriZal HaKadosh.
And here is exactly where the controversy begins.
The Shlah HaKadosh (Tractate Shvuos 47) writes that this order of what to learn has become a Minhag in Klal Yisroel and this is what we learn. The Shvus Yaakov, however, (Chok Yaakov 494) writes that this Tikkun was only enacted for the masses of people, and those that are capable of doing so should learn their own study regimen.
What is the common custom? Chassidim generally learn the Tikkun, but Litvaks generally learn their own study regimen. Sefardim also generally learn the Tikkun, particularly because the Chida writes (Lev David 31) that one should do so. Indeed, he writes that a group of people who changed the study regimen to studying the Rambam did the wrong thing. He compares what they did to building a Bamah – an unauthorized sacrificial platform.
The minhag in virtually all of the Litvish Yeshivos, however, is to study what the Yeshiva itself studies during the regular Zman. What about the Chida’s point against the group of people that studied the Rambam? We should note that this group created a new regimen for Shavuos. They did not continue their regular yearly regimen. Our Yeshivos are continuing their regular regimens.
It is interesting to note that the Vilna Gaon himself learned the Arizal’s special Shavuos regimen. It is also interesting to note that in the time of Rav Aharon Kotler zatzal in Lakewood there were many bochurim that learned Torah on both nights of Shavuos.
So what should one be studying on this night? The Gemorah tells us (Avodah Zarah 19a) that a person does not learn except for where his heart desires. The Yeshivos should therefore continue their practice, and theplaces that study the Tikkun should continue their practice too.
Rabbi Hoffman is a Mechanech in a Bais Yaakov and the former Morah D’Asrah of the Young Israel of Patchogue. He has written Seforim on Hilchos Mezuzah, Lifnei Iver, Chanukah, Purim, Niddah, His seforim have Haskamos from Rav Yisroel Belsky, Rav Malkiel Kotler, Rav Dovid Kviat, Rav Shmuel Kaminetsky, Rav Chaim Scheinberg, and Dayan Roth’s Beis Din. He is also the author of the forthcoming Sefer entitled, “Not Your Usual Halacha.”