From their FAQ:
Plazes adds physical presence to the web. The Plazes website automatically detects your location and connects you to people and places nearby. See people in your area, discover other locations and follow the whereabouts of your friends.
Locations within Plazes are not just global coordinates they carry significance to you and your friends. You can name locations like "Home" or "My Office". Represent your locations by how you relate to them and discover other significant locations.
Relate to other locations by adding pictures, comments, and reviews. Plazes can also be told to remember the locations you visit so you can review your travels.
Now, from the 2nd to the 17th of May (next month) Plazes will have a "sneak preview" for some people (the picture up there is a rip curl on that sneak preview) about the "new Plazes", that will bring some new and hopefully excitant features.
I'm on the previewers list, and have permission to invite some other people into the preview, so... free invites! If you want to have an invite to the new version of Plazes just mail me telling so, and I'll gladly add you to the list. Notice that this is a sneak preview and not a "pre-release" version, so the data you'll add there in the preview phase will not persist and migrate to the final version, once it is released.