I have a MacBook Air with a 64GB SSD.
Quick, light, powerful, a really nice little unit.
But – tight on space. I was recently upgrading to Mountain Lion and I went through to free up space – I was down to 10 GB free, and I felt that was tight. I deleted as much as I could and rechecked – space went down, rather than up. I now had 8 GB free. Huh?
A reboot cleaned up some of that, but still.
I ran:
cd / du -akx | sort -nr | more
and found that MobileBackups was large enough to be of concern. I run TimeMachine to an external 1TB drive, and I don't need or want constant local backups at all.
To disable MobileBackups (local TimeMachine disk usage and backup):
sudo tmutil disablelocal
turns off mobile backups, and on reboot the folder is gone. I can keep approximately 20GB free now. Acceptable.
—doug