Nice little app, does the job. I can't really find anything negative about it, some other programs have some more advanced features but I use this one because it does the job quickly and without any hassle.
One suggestion I have would be to make this donation-ware, simply because there are open-source & free utilities (bcrypt) that do the same thing, in fact, it would not be difficult to write an Applescript in conjuction with these free command line tools could do what this app does. That said, $5 is not an unreasonable price and Crypt2 is probably worth it for the ease of mind of having important files encrypted. Some other nice points are being able to drag'n'drop an encrypted or unencrypted file to Crypt2's dock icon, and that it puts the encrypted file in the same directory as the unencrypted file.
For the developer: Is Crypt2 compatible with other blowfish encryption/decryption programs? Obviously I can't expect for you to have tried every one of them out there, but I was just wondering if there are any oddities with Crypt2 that are different from other blowfish encryption schemes.