After updating iPhone 3G 3.1.2 to iOS4 my HDD space is very low!

[MacBook MH]

Yesterday I updated my iPhone 3G 3.1.2 to iOS4. My Mac's HDD space was 13GB by then. I followed the updating process normally until I got a dialog saying that iTunes will back up all of my contacts,media,calendars.... I clicked continue. The update completed successful, but now my HDD has only 800MB of free space.
I suspect that the backup is very large, but it is not in the MobileSync/Update folder....
Any suggestions?
Thanks,
Martin

 

[Minimoose 360]

Yesterday I updated my iPhone 3G 3.1.2 to iOS4. My Mac's HDD space was 13GB by then. I followed the updating process normally until I got a dialog saying that iTunes will back up all of my contacts,media,calendars.... I clicked continue. The update completed successful, but now my HDD has only 800MB of free space.
I suspect that the backup is very large, but it is not in the MobileSync/Update folder....
Any suggestions?
Thanks,
Martin

Check for duplicates of the data.

 

[MacBook MH]

... i forgot the MobileSync/Backup folder is together only 5.5GB size... but I am missing 12GB of space... +my iTunes Library lays on an external HDD.