Life Imitates Art - Very literal example: the author has actually made the "LOGO" shirt and opaque glasses his Author Avatar wears, allowing him to cosplay has HIMSELF.
Schedule Slip - Officially, the comic updates every Wednesday, but every convention update within memory has been at LEAST a day late. It's not unheard of for an update to not appear until Friday night.
Filler comics aren't immune either. If several conventions are too close to each other (or Real Life is simply getting busy), filler updates have been known to stop entirely.
Write Who You Know - Being based on real life, the overwhelming majority of secondary characters are real people.