For an update and detailed slide show on this feature see: Google Maps: Everyone can create a business listing
I have yet to see the feature but according the blog:
The option seems to work only for the US and you can enter few details about the local business or the place: address, name, phone, website and category. Google promises that “once you save your place, the whole world can find your addition by searching for it within a few minutes.”
Here is a a screen capture courtesy of the Google Operating System Blog:
The posters at the blog wondered about the impact of spam in this user gnerated content and Matt Cutts responded:
I would assume that Google is going to take mapspam quite seriously. I invited someone from the local team to discuss the subject in depth with my entire team just last week, for example, and we talked about lots of ways to work together. So my personal advice would be to make sure that your business name/category is accurate.