[NullSonic]

I just wanted to add my voice to the seemingly very small (as reported on Page 4) percentage of users who still use the Classic interface. I have been a user of Fastmail since 2003 or so (started paying in 2005). At the time I was looking, the (now) Classic interface is the biggest reason I chose FM. It simply excelled above any of the competitors. It had the perfect blend of power and ease of use that I was looking for. It matured over the years to become even better.
Then, the New interface came out. I was excited to try it. I used it, but found it lacking. I was happy when I found I could still use the original interface, and continued to use it.
Over time, I would come back to the New interface, only to find it continued to not meet my needs. I would inevitably switch back to Classic. I thought: I hope the Classic interface will always be available. But I knew that it might not, mainly because of the reasons that have already been stated (maintaining old code, two systems, etc). It's unfortunate.
I will really miss the "keep unread and go to: Next, Previous, N/P Unread, First Last, Folders; Delete and Next/Previous etc." options at the top of messages. I also like selecting a page of emails at a time and deleting or taking action on just that set. I also like being able to move a message to any folder while in a message by clicking on the "move message" button on the left. I like the easy to access Show full header. I like seeing how many emails are in a folder without having to select them all first. These are the things I will miss most. There are other things, but these are invaluable.
I'm sure I won't convince anyone to keep the Classic interface around, but at least I've stated my opinions.
I will miss it, and will grudgingly use the new interface. I will learn the keyboard shortcuts as they seem to hold great power. Who knows, maybe after a year or so, I'll forget I ever loved the Classic interface. Who knows?