  We report experimental observations and numerical simulations of the
formation, dynamics, and lifetimes of single and multiply charged quantized
vortex dipoles in highly oblate dilute-gas Bose-Einstein condensates (BECs). We
nucleate pairs of vortices of opposite charge (vortex dipoles) by forcing
superfluid flow around a repulsive gaussian obstacle within the BEC. By
controlling the flow velocity we determine the critical velocity for the
nucleation of a single vortex dipole, with excellent agreement between
experimental and numerical results. We present measurements of vortex dipole
dynamics, finding that the vortex cores of opposite charge can exist for many
seconds and that annihilation is inhibited in our highly oblate trap geometry.
For sufficiently rapid flow velocities we find that clusters of like-charge
vortices aggregate into long-lived dipolar flow structures.
