I use DropBox for all my music backups that I need.  If I copy and paste a project's folder into DropBox, I think I am achieving the same thing as Gobbler.  The difference is in cost and manually copying and pasting files.  I would love to have DropBox integrated with Sonar.  However, if the cost and efficiency of Gobbler gets better, I will want to research that more.  
 

Can I use a Gobbler with Sonar Platinum?

No. I believe it was discontinued. 

We were told that it was discontinued because Gobbler had moved to version 2 but only release an API for Mac OS X, not Windows.

It's certainly not the case any more because Presonus has Gobbler available in Both Windows and Mac OS X.