• Hover over the title bar
• Click the filename to pull down a menu, enter the new name and hit the return key to save the files name change

The file extension remains consistent with the files format, and unlike renaming things in the Finder you can't accidentally change the file extension too. The usual method of renaming files through Finder is still around, but if you're saving files directly to iCloud this is likely the preferential method.

The first scrolls you all the way to the bottom of the page you're on; the second puts you at the top. So if you need to move in either direction, you don't have to actually scroll at all. For those of you who use Chrome or Firefox, this works in those programs, too.

This little shortcut is good to remember, as you can use it in other places around the Mac. In document-creation apps (like Pages or TextEdit), those shortcuts mean "jump to the beginning or the end of the text". So you don't have to scroll in those programs, either.

Finally, if you add Shift to those shortcuts, it means "select all the text between where my cursor is and the beginning/end". So if you place your cursor in the middle of a document (or select some text on a webpage), Shift-Command–Up Arrow will select everything between your cursor and the beginning of the document; Shift-Command–Down Arrow will select things between there and the end. We use this as an alternative to click-and-drag to select text, and it's more controlled than Select All.

Apparently it happens often enough for there to be an individual keyboard shortcut to instantly swap the last two typed characters, and that keyboard shortcut is Control+T.