Look at your hard drive. Now look at me. Now look at a recent snapshot in your Backups.backupdb directory from after the 10.8.3 release (March 14th-ish); now look at mine. Hopefully, your snapshot doesn't look like mine, because if it did, you'd notice that Time Machine hasn't been backing up /Applications, /Developer, /Library, /System, or /private for the past two months.
Um, what??? There's no setting related to this in System Prefs, and I actually have 10 GB still free on the drive, and I'm reasonably certain this started happening after installing the 10.8.3 update. Except for individual user files, Time Machine is completely useless to me right now and all of the backups done in the past two months are invalid for system restore.
Before 10.8.3:
ligeti:Macintosh HD nick$ cd 2013-03-18-003447/Macintosh\ HD/
ligeti:Macintosh HD nick$ ls -a
. Users
.. Volumes
.DS_Store bin
.DocumentRevisions-V100 cores
.com.apple.backupd.mvlist.plist etc
.file lib
.vbt5 mach_kernel
.vol opt
Applications pbcl.db
Developer private
Games sbin
Library tmp
Network usr
System var
After 10.8.3:
ligeti:Ligeti nick$ cd 2013-03-25-001307/Macintosh\ HD/
ligeti:Macintosh HD nick$ ls -a
. Users
.. Volumes
.DS_Store cores
.DocumentRevisions-V100 etc
.com.apple.backupd.mvlist.plist lib
.file mach_kernel
.vbt5 opt
.vol pbcl.db
Games tmp
Network var
Excuse me while I fire up Carbon Copy Cloner, but does anyone have any light to shed on this? Can anyone comment as to whether they are or aren't experiencing this on 10.8.3?