Before finding the holodeck program, Leah Brahms reviews an engineering log of modifications made to the ship by La Forge. The last entry on the list which is only seen very briefly is "Tonight on HBO."
First appearance of the redesigned Jefferies tubes as they would appear throughout the run of the series and on other star-ships of the 24th century.
Dr. Brahms was to make a third appearance at some point, but Susan Gibney became unavailable due to her becoming pregnant.
In the "sour the milk" discussion it is said that "All matter in the universe vibrates in a specific radiation band. 21 centimeters." The 21 cm. microwave radio wavelength is important in astronomy because it is emitted by changes in the energy state of hydrogen, the most common element in the universe. This microwave 'glow' allows us to see the distribution and movement of matter throughout the visible universe. As for 'matter vibrating', that is a reasonable description of heat. Those heat vibrations are several orders of magnitude smaller than 21 cm.