WordPress.com team has created a new editor for writing blog posts. The previous one was quite fast and responsive. This is more fluid. The options while you are writing a new post like ‘category’, ‘tags’, ‘sharing’ are handy. The most nice feature is the ‘preview’ functionality. It opens a popup windows to show you the post before actually publish it. You can see your post in different screen sizes (desktop, tab and mobile) from that popup window. This is something that was not before and a welcome change.
Currently I am writing this post with new editor.
You can read more about the new editor at official WordPress.com blog.