New features
I logged into my Gmail account yesterday -- yes, it's still in beta -- and noticed a couple of changes that were trumpeted by a link which exclaimed "New Features!" in bright red letters, like so.

I now regret that I didn't take some screenshots the first time I logged in. That would have made it easier to track the evolution of the interface and make it easier to illustrate what I will now attempt to describe with words.

Contacts
The first change I noticed was that the Contacts link ("address book" for users of other e-mail services) had been moved from the upper right to the left column, drawing attention to itself with a "New!" red text flag. Click the link and the yellow-bordered Contacts view replaces the Inbox view.

The ability to search those contacts and search your Inbox for all messages from a person with one click on your Contacts list is a useful feature that will surely be replicated by Microsoft Hotmail and Yahoo in short order.

Atom XML feed, Gmail as platform & authentication
The other notable change was the addition of an Atom button/link at the bottom of the left column, beneath the Labels menu item. (The button is gone now, which makes me regret not taking the screenshots all over again.)

Presumably the link is to let end-users view their Gmail inboxes with a standard newsreader or integrate their e-mail into a blog, intranet or custom Web page using an Atom XML feed.

It may not be for everyone but a subset of the technologically-inclined -- who presumably are the majority of Gmail users -- will love this feature.

I have a hunch that the Gmail Notifier application that sits in the Windows system tray and alerts users to new mail pulls its information from an Atom feed. Independent programmers have already come up with all sorts of unauthorized hacks that use Gmail, so the unveiling of the Atom feed looks like an opportunity for those programmers to develop new hacks with the tacit permission of Google. This is a smart move that in a small way sets the stage for Gmail to become a platform upon which third-party software and services are based. We have already seen it on the search side with the Google API.

I have some questions and concerns about how access to the Atom XML feed will be restricted, how authentication of its users will work and how integrity of that information will be maintained.

Invitations link, interface consistency & design methodology
A pseudo-cosmetic change includes the removal of the blue bar across the top of the interface that exhorted me to "Invite x friends to Gmail" (where x represents the number of Gmail invitations I had left to distribute). It's been changed back to some red text in the left column as it was before. The thing that I find interesting about this is -- to the casual observer -- it almost seems as if the human-computer interface designers are engaged in a tug-of-war about where to put particular elements.

The more likely case is that the designers are testing different iterations of the interface to determine which design and placement appeals to the widest possible audience.

While testing multiple designs of an interface is a standard method to determine which design is best, switching back and forth is a bad idea. Changes of this sort are usually an unwelcome surprise to end-users. In this case it means a relatively minor adjustment to the way specific functionality is accessed and a particular feature is used. In the general sense it can be a confusing and frustrating experience when parts of the interface keep moving around and the user has to repeatedly relearn how to use a product or service. Imagine if the interface on your favourite piece of software changed every two months and menu items shifted around, or if the layout of the dashboard in your car changed every few months.

There is an expectation of consistency by end-users.

Forwarding & Drafts
Some not-so apparent changes include the ability to forward Gmail to another account and the ability to save drafts, which Google admits should have been in there from the start.

An excerpt from the Gmail Help Center (hyperlinked bullets/headings are my edits):

Some features we know you've wanted (and one we should have had all along):

• Gmail Notifier
  Want to know if you've got new mail? Let us do the checking so you don't have to. Find out when new messages arrive, and even see their subjects, senders and snippets, all without having to open a web browser. Learn more
• Search your contacts
  With the new and improved Contacts list, search for a contact as easily as you would a message in Gmail. Add notes and phone numbers. View messages directly from the Contacts list. Stay in touch with the people in your life more easily than ever before. Learn more
• Automatic forwarding to another email account
  We're testing a new feature that lets you forward new incoming messages to any email account you want. It's free during the test and you can set it up in seconds. Even set up filters to forward only some of your messages. It's your mail. Get it the way you want it. Learn more
• And finally... Save Drafts!
  For when you can't find the right words, save drafts and find them later. Learn more