I just got the answer. It's called RVSM and here's the information:

a.. The implementation date/time is January 20, 2005 at 0901 UTC.


a.. On the same date and time and at the same flight levels, Canada and
Mexico will implement RVSM. Canada implemented RVSM in its Northern Domestic
Airspace in April 2002 and plans to expand RVSM into Canadian Southern
Domestic Airspace in January 2005.


a.. The RVSM program enables vertical separation to be reduced between FL
290-410 (inclusive) from 2,000 ft. to 1,000 ft. RVSM was first implemented
in North Atlantic Airspace in 1997. It is now implemented in other major
airspaces such as Europe, the Pacific Ocean and Australia.


a.. The goal of DRVSM is to provide user and provider benefits in domestic
U.S. operations that have been enjoyed since 1997 in other world airspaces.
RVSM makes six additional flight levels available for operations between FL
290-410. It has been show to: enhance aircraft operating efficiency by
making more fuel/time efficient flight levels available; enhance air traffic
control flexibility and provide the potential for enhanced enroute airspace
capacity.


"Chuck Dreier" wrote in message
k.net...
I just returned on a flight from San Juan to Orlando and our flight level
was 300, including a portion over the mainland. Since then I've been
listening to my aircraft radio and routinely hear flights assigned FL320,
340, etc.. It was always 2000 feet separation with levels 290, 310, 330,
350, 370, etc. What has changed, and when did it change? Thanks!