Google has added more search by number features:
Area Codes, e.g. 650, bring up maps.
Flight numbers, e.g. usair 50, provide links to flight tracking
Vehicle ID (VIN) numbers, e.g. JH4NA1157MT001832, link to a CARFAX report on what kind of car and its status.
U.S. Postal Service tracking numbers link to package status.
Source: Google Weblog