  It has been suggested that circumstellar disks evolve from dense, actively
accreting structures to low-mass, replenished remnants. During this transition,
grains may assemble into planetesimals, or the disk may be cleared by newborn
planets. Recently identified nearby groups of young stars provide valuable
laboratories for probing disk evolution. I discuss the properties of dust disks
in the TW Hydrae Association and the MBM 12 cloud, and compare the results to
other studies of disk evolution and planet formation timescales.
