I recently discovered that Safari supports simple drag navigation around large pages rather line Photoshop's space-drag functionality: by simply holding ctrl and moving the mouse (not dragging -- the mouse button remains up), the cursor changes to a hand which grabs and drags the page. Perhaps I'm really late to the game on this one, but I'm totally hooked.
I've been finding, however, that I'm so attached to this mode of navigation when reading in Safari that I'm constantly subconsciously trying to do it in all sorts of other apps. I personally think this would be a fantastic way to browse text in TextMate. Like all good programmers, I'm of course completely attached to the keyboard when actively developing, but there are many times when trying to figure out some code or reading a README is much more like browsing than active development, and in these situations I'd really love to have this sort of interface. It's particularly great for trackpad (or wacom tablet) use.
Far from super-high priority, but at least worth a brief thought, as it's probably not the most challenging bit of polish to add. -jrk