Google is in the business of answering Gmail prayers, and business is good.
Nearly two years ago, in On using Gmail exclusively, I said the following:
If you are reading a “conversation” and see that a new e-mail has arrived, it would be nice if when that new e-mail is part of the conversation you are currently looking at, it would just refresh your conversation instead of requiring you to go all the way back to the list of conversations and click it again.
That request has been fulfilled (as have many others from that post), because, as I noticed earlier tonight, Gmail now displays a small rectangular box in the bottom, right hand corner of the browser window when the above-described situation occurs.
Inside the box it says "New Message from John Doe" and offers you two choices: "Update Conversation" and "Ignore." As you might expect, when you tell it to update the conversation, it refreshes the message-body window with the new e-mail. It works great.
Speaking of working great, it would be remiss of me to not mention the speed bump this version has received. I mean, wow.
[W]e [now] prefetch messages in the current view, so when you open an email your browser doesn't have to talk to Google's server; it just displays the message. These techniques really shine on newer browsers and computers. […] We're seeing sub-200ms times when opening messages — pretty quick.
Pretty quick indeed. I'd call it instantaneous. If you didn't know you were working from within a browser, you couldn't be certain either way.
Unfortunately, even in light of these big improvements, I'm still forced to use the "old" version (which is available by clicking "older version" in the menu at the top) because the Gmail Macros Greasemonkey script isn't yet compatible with the new version, and I can't live without it.
True, the keyboard shortcuts were updated in the new version, but they still won't let me add/remove labels and quickly move back and forth between them. My workflow depends on that sort of functionality being there; without it, I feel horribly inefficient, which negatively affects my mood.
Google has "contacted a number of the developers behind some popular extensions and provided them with an opportunity to create fixes," and so I'm sure I'll be able to really enjoy the new version soon enough.