Like everyone else here I also noticed the size occupied by the mobile backups. I have a MacBook Pro with a drive of 750GB. When I check the available space via the Finder it says I have 380 GB free. But then a widget I have says I have ony 178 GB available. A little investigatioin showed that the difference is taken up by the mobile backups (which appear as a virtual drive in /Volumes: /Volumes/Mobilebackups).
I am not worrying about that since that space will be freed up and used for other stuff if I need it. I may still turn off time machine backups while away - I will actually be away for another two weeks - three weeks in total - before connecting back to my Time Machine backup drive at home.
As for all those complaints about the "other" category in the disk use, my use is like this at the momebt:
Audio = 4.83 GB
Movies = 4.81 GB
Photos = 8.99 GB
Apps = 10.02 GB
Backups = 204.65 GB
Other = 340.22 GB
So do I worry about all the "other" space ? Not at all. I obviously use this device for other things but music, movies and photos. I happen to use it also for real work, which includes storing many documents and files, presentations, spreadsheets, manuals, software installation kits and (the big consumers) a number of big virtual machines (Linux and Windows).
The bottom line is that, unless you use your Mac exclusively for entertainement (listening to music, whatching movies, editing photos, capturing audio, ...) you are bound to have "other" data. I see nothing to worry about.
On a more general note of Time Machine and mobile back ups, I will probably end up turning them off. Backups serve two purposes not to be confused (and Time machine does confuse them)
1) one is to protect from catastrophic media losses: this include a simple failure of your internal disk drive, but also your mac being crushed in some accident, or being stolen. And obviously recovering from those can only happen if you have your backups stored elsewhere on a different external media (obviously NOT on the same drive) and kept in a different place - i.e. don't take it with you on the road. Don't leave it at home next to your mac (both will get burned or stolen together if that ever happens). Best is to keep it at another place: your professional office if you have one, or your mom's place.
Obviously this will not be a perfect up-to-the minute backup: all you can do is to restore to a state from your latest TM backup on the external media.
And again, mobile backups do not help here after a total media loss.
2) the other is to protect from human / software mistakes. This is where you want to recover previous versions of documents, source code, executables before you messed them up or before you installed that new version. For that the mobile backups are extremely useful since you can go back to an earlier state immediately, using the data that time machine conveniently saved for you automatically. There is no need to wait until you are back home to try and restore those old versions. Obviously Time Machine can only store so much, based on your available space, but this is still a great feature, especially since taking those backups is very unobtrusive.
Albert
