Drive space usage is greater that sum of folder space

Question

I just created a new boot disk and then restored files from Time Machine. didn't restore everything, which would have amounted to about 248 GB. But when I look at the information (Get Info) for the drive under Devices is is currently showing that the space being used is 334,733,254,656 bytes (334.73 GB on disk)
I checked the information for each of the folders and files in the root directory and the sum of there usage is roughly 90 GB:
Applications 
18,903,169,688 bytes (19.84 GB on disk) for 21,428 items
Developer
15,963,571,487 bytes (16.55 GB on disk) for 160,773 items
Users
12,062,054,006 bytes (12.17 GB on disk) for 20,478 items
Library
9,983,670,968 bytes (10.39 GB on disk) for 99,598 items
System
5,487,399,383 bytes (5.93 GB on disk) for 97,334 items
MSI
3,576,714,672 bytes (3.59 GB on disk) for 8,106 items
private
5,261,118,622 bytes (5.26 GB on disk) for 1,077 items
lost+found
4,050,591,911 bytes (4.05 GB on disk) for 2 items
The other folders don't show much usage.
I restarted the computer and it still shows the same thing.
I'm skeptical about the 334GB. What can I do to find out what's right and reconcile it if there is an error?

Answer 1

See my FAQ*:
http://www.macmaps.com/diskfull.html