I've always aware of reserved blocks on an EXT filesystem ( and on NTFS as well ) - probably this is one reason for newcomers to choose ReiserFS instead. For them, I'd recommend btrfs1, but for those of stability junkies and EXT lovers: on every non-system disk this is truly safe to do, and you'll not regret it.
When you format a partition to EXT, the filesystem reserves some space to store system things inside it. It's also a kind of stability issue, an inside swap if it pleases - but there's no need for it on non-system disk. This usually takes 5% of the formatted disk capacity - as for 1 TB disk it's 50GBs !!
Now, to reduce it:
sudo tune2fs -m 1 /dev/[your device]
This sets the reserved blocks to 1%, therefore on a TB disk to 10GB. It's still much, I know, and in some cases it's safe to reduce it to 0, but just to make sure everything is working fine, I left it on 1%.
See what you gained:
As for Truecrypt devices: When you mount a truecrypt partition ( or full disk ) there's going to be a
/dev/mapper/truecryptX, where X is a number. Use this instead of