In the Apple ecosphere—especially in iOS—a convenient short cut is to type two spaces to end the current sentence and start a new one. Specifically, two spaces will delete the spaces, insert a period and a space, and capitalize the next letter. There’s probably something similar in the Android world; it seems like a natural thing to do.
Over at Bicycle For Your Mind, macosxguru has a post that describes three of the recent changes he’s made to his Emacs environment. Two of them—showing tabs and newlines explicitly, and fiddling with his mode line probably won’t interest most Irreal readers. The third is importing the two space shortcut into Emacs.
Emacs, of course, doesn’t have that capability but macosxguru added it with a bit of Elisp which he binds to the Space key with the text-mode hook. It looks for two consecutive spaces and repaces them with a period and space. The tricky part is capitalizing the next letter. He does that by reading the next character explicitly and capitalizing it if it’s a letter. He also checks for some special keys (like an arrow key) and “unreads” them so that Emacs can treat them normally. All the code is in the post so see it for the details if you’re interested.
I’m ambivalent about this change. On the one hand, I use it all the time on my iPhone and iPad but that’s because typing is such a pain on virtual keyboards. On a regular keyboard, I’m pretty sure that I could type the period, space, and next letter just as fast. The shift for the next letter might slow things down a bit but not by much. I haven’t decided yet whether I will adopt it but inertia will probably cause me not to.