is it legal to have a valid drivers license in more than one state? 
Does military service affect any pertinant laws?  For example, I had,
until today, a valid license in Maryland which is my state of legal
residence.  I pay taxes in Maryland.  I am in the military stationed
in Virginia, and went to the DMV to get a Virginia license which was
necessary prior to getting a motorcycle permit for Virginia.  When I
had obtained the Virginia license, the lady at the DMV wouldn't give
me my Maryland license back.  Some other conflicting information
between her knowledge vs. the paperwork she gave me, lead me to wonder
if she had the facts straight.  I've looked online and found various
state's laws that prohibit "possessing multiple licenses" but could
refer to possessing multiple licenses from the SAME state.

The Virginia DMV clerk was operating under Virginia law. In order to
obtain a Virginia driver's license, you must surrender your license
from another state. I am not aware of any state in the USA which does
not follow this procedure. If you do surrender your license from out
of state, it's a very good idea to keep a photocopy of it. Often the
DMV office has a photocopier which can be used for this purpose.

However, your military status does make a difference, as mentioned below.

"New Residents: 

Within 60 days of moving here, you must obtain a Virginia driver's
license. However, if hold a commercial driver's license (CDL), you
must obtain a Virginia CDL within 30 days.

If you hold a valid driver's license issued by a U.S. state,
territory, jurisdiction, a Canadian province, France or Germany, you
may not be required to take the two-part knowledge exam or the road
skills test, but you must pass a vision screening. Canadian or U.S.
licenses must be surrendered when you apply for a Virginia driver's
license. Be sure to photocopy your out-of-state driver's license
before surrendering it -- you may need it for insurance or licensing
purposes."

Virginia Department of Motor Vehicles: Driver License Eligibility Requirements
http://www.dmv.state.va.us/webdoc/citizen/drivers/eligibility.asp

"The first thing you must do when you move is to apply for a Virginia
driver's license. If you are currently licensed out of state, you must
surrender your license when applying for a Virginia driver's license."

TRAFFIC LAWS IN THE STATE OF VIRGINIA
http://www.discountdrivingclinic.com/topics/English/topic11.html 

"New Virginia residents must pass an eye test and surrender their
valid driver's license from another state."

Washington County Vehicle & License Information
http://www.washingtonvachamber.org/autoinfo.htm 

That was the bad news. The good news is this:

"If you are an active-duty member of the Armed Forces stationed in
Virginia, you, your spouse and dependent children 16 years and 3
months of age or older may drive with a valid driver's license issued
by your home state or country. Vehicles registered in your name may be
driven with valid out-of-state license plates if you are the sole
owner. If the vehicle is co-owned, all co-owners must be active-duty
members of the Armed Forces. You may register your vehicle in Virginia
without obtaining a Virginia driver's license."

Virginia Department of Motor Vehicles: Driver License Eligibility Requirements
http://www.dmv.state.va.us/webdoc/citizen/drivers/eligibility.asp

In view of the above, if you are an active-duty member of the military
stationed in Virginia, and your motorcycle's license plates and your
driver's license are issued by another state, you are not required to
obtain a Virginia driver's license nor to obtain Virginia license
plates.

This was the search string that gave me the best results:

Google Web Search: virginia  "driver's license"  "another state" OR
"out of state" surrender OR surrendering
://www.google.com/search?hl=en&ie=UTF-8&q=virginia++%22driver%27s+license%22++%22another+state%22+OR+%22out+of+state%22+surrender+OR+surrendering

Please keep in mind that Google Answers is not a source of
authoritative legal advice; the material I've posted above is intended
for informational purposes, and should not be viewed as a substitute
for the services of a qualified legal professional.

I hope this helps. If anything is unclear, or if a link doesn't work
for you, please request clarification; I'll be glad to offer further
assistance before you rate my answer.

Best regards,
pinkfreud

That was just what I was looking for.  Thanks!

Possibly you should have registered the motorcycle in Md even tho it
was in Va.  Did you call the Md DMV?   Otherwise, Md might want sales
tax if you later reregister the motorcycle in Md, since you were
always an Md resident.