I can verify that this site is wonderful and good after easily creating my own google map hack. Just in case you are curious where to find feral cats in Sacramento, well, try here. I know you've been curious.  Anyway, I'll let them tell you (via their 'about' section) why they're so cool:

Wayfaring hopes to be a great resource for people who want to build personalized maps, and share them publically or privately. When we first started talking about building this site, we just wanted to make it easier to find activities around the globe through this map and destination sharing. What bar should you go to while waiting for a table at your favorite restaurant, for example? Just simple things like that so traveling can be a little easier.

Much like Wikipedia, the value or goodness that will come from this site will come from those who use it. Almost everything can be edited and changed, so be good to each other. The trip you save might be your own.

To see an example of how this site is best used, try checking out the Best of Wayfaring!