Warning: this review covers only security, and is not concerned with interface, usability, and other issues.

Algorithm Security:

The program encrypts each character by rotating it by a corresponding character in the password (starting over from the beginning of the password when it gets to the end). It also obfuscates each character by probabilistically turning it into two characters, but this process is trivially reversible, and adds nothing to security. An attacker could easily retrieve the key if he knows part of the message, and could use linguistic analysis to easily crack the key if the message is longer than the key or a key is used multiple times.

Key Security:

The key is used in a very simple way, with the effect that if the key has low entropy (as most passwords do), it introduces severe weaknesses that could allow an attacker to guess at the key and message.

Side-channels:

This program uses local variables for sensitive data and cleans up after itself well, leaving no traces that would compromise it's security.

Overall:

Not recommended. While this program employs an algorithm that is good for one-time-pad encryption, it does not employ it in a secure way. An attacker who gains access to your data vault could retrieve it's contents and your key with ease.