If you don't sign your keys in GnuPG you'll get an error when encrypting that reads "There is no assurance this key belongs to the named user". If you get this error, you can correct it by signing the key with the following command at the command prompt:

gpg --sign-key user-id

where you put in your user-id. When you do this, it signs the public key with your secret key. Once you do this, you should be able to encrypt without getting the error.