Starting in 1.0.4, the launcher's new auth system no longer works. Even if it says "Play" (indicating that your access token is valid, which in 1.0.3 it usually isn't), it logs you in offline. The only way to get it to work is to manually retype your credentials every time you log in. The new auth system in 1.0.3 was decent albeit buggy at times, this has gotten to the point that I want to quit Minecraft.