We have recently identified a previously unknown radial migration mechanism resulting from the overlap of spiral and bar resonances in galactic disks (Minchev & Famaey 2010, Minchev, Famaey et al. 2010). This new mechanism is much more efficient than mixing by transient spirals and must exist in all barred galaxies, such as our own Milky Way. The consequences of this are a strong flattening in the metallicity gradient in the disk, an extended disk profile, and the formation of a thick disk component, all taking place in only a couple of Gyr. This timescale is drastically shorter than previously expected and thus can put strong constraints on the longevity, strength and pattern speeds of the Galactic bar and Spiral Structure. Unlike mixing by transient spirals, migration from resonance overlap works also in low-mass systems, such as NGC 300 and M33, and can thus explain the extended disks seen in these galaxies.