After a whole year in development as a user script (initial mention, formerly known as "Github: unfold commit history"), a brief test-drive as an Opera extension at the 2010 add-on con, I finished up the missing bits and pieces to make today's Github Improved! chrome extension available in the Chrome Gallery / Web Store (1.7 now also available in the Opera extension gallery).
New since last release is the little tag delta (Δ) links that let you instantly see what happened between, say, Greasemonkey 0.9.5 and the previous release tag (it recognizes anything where the only thing differing between tags are their numeric parts, which also means it's not going to handle fancy 1.6rc1 type tag names littered with semantic non-numeric parts):
And, as prior users may find even more importantly, that it doesn't hog any shifted keyboard shortcuts, which for some reason had the side effect of making arrow up pull in a pageful of diffs.
Full documentation of all features, and a few screenshots, is available on the Chrome Web Store page. I also take every opportunity to mention that it really shines best together with the AutoPatchWork extension, or something equivalent which unfolds the commit history pagination as you scroll off page. Enjoy!