Finger prints, iris scans, facial features, vein pattern and now walking styles can be used to recognize individuals.

Nikkei.Net (Subscription) reports about a system developed by University of Tokyo's Center for Spatial Information Science (site) that can identify individuals based on their walk pattern in crowds.
The walk pattern recognizer combines floor-level laser beams with overhead cameras to isolate and track individuals.
Tests showed that monitoring 600m2 of a crowded train station, the system succeeded in isolating 80% of 150 poeple.
The system can be used to spot suspicious persons or measure performance of ads or signs in public spaces.
I do not think the system can identify a specific person by his or her walking style. See also the Omron Face Walker.