In addition to previous post, about creating Google Buzz groups. It turns out that Gmail already has a built-in group for Google Buzz and other services. However, these're not visible in Gmail's new contact manager, but viewable in the older Gmail. Since the group doesn't have a name and are hidden, you can't use to send email or post private Buzz, but you can select all contacts and add them to another group.
And a hidden group for Google Latitude friends, includes people who can see your location in Latitude.
Another group lists all your Gmail Chat/Google Talk friends. Some of these people were automatically added by Google if you didn't disable "Automatically allow people I communicate with often to chat with me and see when I'm online" in ettings.
Finally, if you miss "all contacts" group in new contact manager, here's a built-in group that includes both people you've manually added ("my contacts") and people automatically added by Google ("other contacts").