A script finds out how much recovery points volumes could be shrunk on DPM2010. One word of caution though: use the shrink feature with common sense and not as a regular remedy! Repeated small shrinks cause free space fragmentation and increases the number of extents. The shrink option can be useful if accidental gross over allocation occurred that certainly is not needed. Or if storage pool is depleted, no chance of rapid expansion and urgent need of raw space.
More info: Find the script here.