1. "less" scrolling in gnome-terminal. When you less something, the mouse wheel actually scrolls the less output. I can't tell you how insanely useful this is when debugging.
2. The up button for epiphany. Seriously. For months, I've been cursing web browsers, wishing they had an up button. Then shaunm told me epiphany did. Immediately, my browsing life has become so much better. Every program should have an up button (it's in the customise toolbar if you're interested).
Anyone else got other hidden cool features in GNOME that would make my life rock even more?
(This post brought to you by the power of waiting for jhbuild to compile something ... anything)