Not the best spot to post this here, but I'll explain.
In Windows MBP, when you loaded the game, there would normally be a "Leaderboards" button near the bottom right. Previously, you would create an account on "PhilsEmpire", an affiliated site, where you would then log into the leaderboards with it and play "online". With MBP 1.50, this was changed so that the new MarbleBlast website would be able to host the leaderboards without a separate server. The leaderboards also came officially to both Windows and Mac platforms.
The point of the leaderboards is to be able to play online for competitive play. Upon logging in with your username and password for the site, you would access a chat room and numerous other features to the game. When you play levels there, your time and achievements are tallied and "ranked"; that is, a numeric score is determined for the times you achieve online for each level you play. The idea is that your "rating" as it is computed is totaled for the levels you complete and achievements you (secretly) receive, where your rating is then listed on a global "leaderboard" to show your performance to other players. If you beat and improve your times, you will earn a higher score, and be ranked higher on the leaderboards.
Of the more recent and newer features that come with MBP 1.50, you can play against others in more competitive ways, such as challenges/super challenges, and most of all, by playing multiplayer. With the next build of MBP 1.50 being a release candidate, you will be able to hopefully read all of this in the manual, as well as being able to experience all of MBP's new features.
Hopefully this offers a mostly complete explanation to what you're asking. While I typed, Regislian may have snuck in a more concise explanation. As a final note, you can access these leaderboard rankings by the "Scores" menu at the top.
~ PM