The theme is "the highschool years." The plan was to make one icon from every episode of the first three seasons. Then the plan became two icons from every episode. And then the plan turned into just getting all the screencaps I liked and making as many icons as possible before today. Season 3 is under-represented, but whatever.
ETA: Incase anyone's interested, the lyrics in 65 and 66 are from "I Will Love You" by Sarah Slean; 98 from "Bed of Lies" by Matchbox Twenty; and the text in 100 is from something by Shakespeare, a play, I forget which one.