On the Shabbos before Rosh Chodesh Sivan, אב הרחמים is said [before Mussaf].1

On the Shabbos when Parshas Bechukosai is read, the reader makes the blessings over the third portion without being called to the Torah.2

No Tachanun is said [from the Minchah preceding Rosh Chodesh] up to and including the twelfth of Sivan.3

The Rebbe Rashab did not look favorably on the practice of taking a haircut [at the conclusion of the period of the Omer] during the Three Days of Preparation (Shloshes Yemei Hagbalah) before Shavuos, i.e., before the eve of Shavuos.4

It was the custom in Lubavitch to stay awake throughout the [first] night of Shavuos.5

During the public reading of the Ten Commandments [Aseres HaDibros; i.e., Shmos 20:2-14], the congregation stands and faces the Sefer Torah.6

The hymn entitled Akdamus is not said.7

Since Shavuos falls not on a named date, but on the fiftieth day of the Omer which each individual is obligated to count independently, a person who gains or loses a day by crossing the international dateline during Sefirah has the problem of when to celebrate Shavuos.8