For me Flickr made this popular with the rotating "Welcome [username]" upon logging in. They took a fun little spin with it by randomly alternating the salutation's language to the experience as well. A few example salutations you may receive upon a Flickr's welcome page refresh - "Moyo montylounge!", "Konnichiwa montylounge!", "Bangawoyo montylounge!".
Another successful implementation of getting personal can be found in the popular project management web application - Basecamp. By allowing users to customize the color scheme, and even add a logo to a project's title area, Basecamp allows its users to further customize the experience to more closely resemble their client's brand. I relate this to the equivalent of remembering a person's name the second time you meet - it makes the person feel a little more special and hopefully an immediate respect is returned.
For those creating Django applications, I discuss a the starting points for getting personal in my post Customizing the Django admin - Branding.