A MAC computer is always sitting on the desk (although never used) where Leonard wants to place the dining room table. It was removed, and replaced with an older system so Sheldon could go back to Windows 98.
Sheldon compares himself to a frog in a glass of water, slowly boiling to death. This is a scientific story to illustrate how organisms only respond to sudden changes, but not gradual ones: a frog placed in a glass of boiling water will immediately jump out, while a frog placed in cold water that is slowly heated will supposedly remain in there until it boils to death. However, this is a complete myth: every normal frog will jump out of a glass of water as soon as it becomes too hot, way before boiling.
Title Reference: The sides that everyone takes when they discuss getting a dining room table for the apartment.
Sheldon mentions Arthur Dent from The Hitchhiker's Guide to the Galaxy (2005), lying in front of the bulldozers to protect his home. Leonard says that Arthur's point was moot because Earth was destroyed by an alien fleet several minutes later anyway. What Leonard doesn't mention is that before that, Arthur was lured away by his friend Ford (who knew the destruction of Earth was imminent) and the house was demolished before Earth was destroyed. In similar fashion, Leonard and Penny (somewhat inadvertently) distract Sheldon from the table issue by reminding him of how his relationship with Amy has changed him.
Amy compliments Sheldon on being funny on purpose, something he was trying to achieve four episodes back, in The Hesitation Ramification (2014).