  In hep-th/0412322, Gaiotto, Strominger and Yin proposed a novel way of
counting black hole microstates by counting the quantum mechanical ground
states of probe branes placed in the near-horizon black hole background. We
discuss the generalization of this proposal to the case of two-charge D0-D4
`small' black holes in type IIA. We also describe the construction of BPS
D-brane probes in the near-horizon region of the 2-charge D1-D5 system in type
IIB. Based on hep-th/0505176, hep-th/0607150.
