The only true way to have security when inputting the master password would be with a hardware biometric identification device that goes from your body straight to a pseudo-keyboard kernel-mode driver, and that will protect you from the script kiddie next door, but if someone really wants your master password, they can get it... Criminals can put a gun to your head, any government agency can get it in the US, if they think you are a threat to national security, clipboard contents can be intercepted, On Screen Keyboards can be easily hacked (read button text on click). But there is light at the end of the tunnel, and it is not a train heading your way: because Linux is not being adopted at the rate it deserves by the general public, the development of malware for it is more or less at the level it was 5 years ago, with most security exploits going towards things a home user would never come in contact with, such as sendmail, httpd, etc.
Edit: I just wrote this and didn't see Eric's comment above mine... and he's absolutely right... Wonderful program, BTW...
