Google has announced a new method of composing and replying to emails; now a chat-like window will pop up and allow you to refer to existing emails and so on while you are composing, which sounds like a good idea. From the official blog:
The new compose pops up in a window, just like chats (only larger). This makes it easy to reference any other emails without ever having to close your draft. You can even do a search or keep an eye on new mail as it comes in. And because the compose window works the same way as chats, you can write multiple messages at once and minimize a message to finish it later.
We're rolling out a preview of the new compose and reply today. After we've added some finishing touches over the coming months, we’ll enable it for everyone.