Likely its running out quicker and quicker.
Don't believe the Apple fairy-tale that Versions is an efficient way of storing your data. It's not.
If you want to reclaim all that space, go delete the .documentrevisions-V100 folder in the root directory of your hard disk.
Be aware that this will delete ALL Versions for ALL apps that support Versions.
To do that, you need to enable the root user, show hidden files and change the permissions on the folder. Here's how:
1. Show hidden files
In Terminal (Applications > utilities) type
defaults write com.apple.finder AppleShowAllFiles YES
(press Return)
killall Finder
(press Return)
2. Enable root user
Go to > System Preferences...Users & Groups
Click 'Login Options'
Click 'Network Account Server: Join'
In the resulting dialogue box, ignore the text input and click the button below, 'Open Directory Utility'
Click the padlock at the bottom of the next box and enter your admin password.
At the top menu bar of Directory Utility, choose the 'Edit' menu > Enable Root User
If you are requested to set a password for it, set the same one as your Admin password (this ensures you won't forget it).
3. Change Permissions
Now go look in the root directory of your hard disk.
You should see a greyed out folder called 'DocumentRevisions-V100'. If it has a 'no entry' icon on it, click the folder and press 'Cmd-i' on the keyboard (or right click the folder and choose 'Get info').
Scroll down to the bottom of the box, click the padlock, and enter your admin/root password. Change all the permissions to 'read & write', and click on the 'gear wheel/cog' and choose 'Apply to enclosed items'.
Choose 'OK' in the warning dialogue box that appears.
4. Deleting Versions history
Now you are ready to go and look inside the Versions directory. I recommend you have a nosey about and check the file sizes both of the folder itself and of the individual contents. Now, here's warning: you can't just delete some of the contents in the folder. If you do, in about 24hrs Lion will see that the folder is corrupt and mark the whole thing as 'bad' and make a new Versions (.DocumentRevisions-V100) folder. What this means is that you will lose access to Versions in the UI, but you won't get your disk space back as it won't delete the 'bad' folder.
The only option is to either lock the thing back up and leave it alone, OR delete the entire .DocumentRevisions-V100 folder with all its contents. What happens then is that Lion will make a new, empty folder to replace it, and start filling it up with versions you make from then on. You'll have reclaimed your disk space (and removed all your previous versions), but you'll need to keep doing the same process at regular intervals.
NOTES
a. No, this does not affect your original saves or any duplicates. Only the versions.
b. Messing about as a root user can have serious consequences if you **** with other stuff. Do as the instructions above say and nothing else unless you know what you're doing. After you've deleted the Versions folder and emptied the trash, go back to Directory Utility > Edit and disable the root user.
c. To stop seeing the hidden files, type the same command as given in 1. above into Terminal, but change 'YES' to 'NO'. Don't forget to do the 'killall' command afterwards.
