I keep hearing about how great walking is, and I'm all for it, but I'd
like to have some authoritative sources. Are there any scientific
articles to back up (or refute, or temper) the "walking is the best
exercise" refrain that I keep hearing all over the place? The sheer
popularity of this idea is making it a little difficult for me to sift
through all the chafe.

For bonus points, get me a source on this: I recall reading that
humans are good at walking compared with other mammals(?), whereas
we're lousy at pretty much every other kind of locomotion. Is it true?
Who says?

Hi brainheart-ga,
 
Walking is considered to be "the ideal exercise" because it
 
- can be done by most people
- doesn’t take any special equipment
  (other than appropriate clothing and comfortable shoes)
- can be done just about anywhere
 
and most importantly studies have shown that walking provides a
plethora of health benefits, comparable to more vigerous exercise
without the health risks.
 
There are many studies that back up this position. Below are two
articles that summarize over a dozen recent research studies, showing
that walking can provide the same benefits as more vigerous exercise,
as well as the many specific health benefits of walking that have been
published in recent years.
 
By far the best source was a huge pull-out walking section in the
Washington Post from a few months ago with a plethora of articles on
the health benefits of walking. The lead article can be found at:
http://www.washingtonpost.com/ac2/wp-dyn?pagename=article&node=&contentId=A17484-2002Sep28&notFound=true
 
What would be of most interest to you is their summary of  ten major
walking studies, which can be found at:
http://www.washingtonpost.com/ac2/wp-dyn?pagename=article&node=&contentId=A17494-2002Sep28&notFound=true
 
To "summarize the summary" these ten studies show walking is shown to,
..."significantly lower the risk of heart attack, diabetes, stroke,
osteoporosis and breast and colon cancer while reducing weight,
cholesterol levels, constipation, depression and impotence and also
increase muscle mass, flatten the belly and reshape the thighs even as
it reduced the risk of age-related dementia"
 
In addition, USA today published a summary of the research supporting
walking in 2000, "Walking works health wonders". It can be found at:
 
http://www.usatoday.com/life/health/doctor/lhdoc124.htm
 
It also covers heart attack, diabetes, stroke, osteoporosis, mental
health, as well as Glaucoma.
 
For more details on some of the studies see:
Breast Cancer: 20% reduction 
http://walking.about.com/library/weekly/aa110199.htm
 
Diabetes: 50% reduction
http://www.healthcentral.com/news/newsfulltext.cfm%3Fid=19782
 
Heart Disease: 30-40% reduction
http://www.healthcentral.com/drdean/deanfulltexttopics.cfm%3Fid=15892
 
As to  humans being better at walking, unfortunately  the price of
your question doesn't leave much room to cover this area, but here are
a few quick links, as well as search strategy that you may find to be
of use.
 
An article on primates explains that humans are unique in having a 
parallel big toe that makesus better at bipedal walking than other
primates:
 
http://www.mc.maricopa.edu/dept/d10/asb/primates/brains.html
 
"Humans on the other hand cannot use their feet for grasping objects.
Our foot is designed for bipedal walking. In order for us to be good
at walking the way we do, our big toe is parallel to the other toes ."
 
An article on human evolution and australopith (early human) evolution
also explains some of the other anatomy differences that hvae evolved
to make us better walkers.
 
http://www.mnh.si.edu/anthro/humanorigins/faq/Encarta/primates.htm
 
"The australopith pelvis overall had evolved a more bowl-shaped 
appearance, which helped support the internal organs during upright
stance. The upper legs angled inward from the hip joints, which
positioned the knees to better support the body during upright
walking. The legs of apes, on the other hand, are positioned almost
straight down from the hip, so that when an ape walks upright for a
short distance, its body sways from side to side. The australopith
foot was also reshaped, including shorter and less flexible toes than
an ape's, which provided a more rigid lever for pushing off the ground
during each step. "
 
Search terms for humans being good at walking:
health benefits of walking
://www.google.com/search?hl=en&ie=ISO-8859-1&q=health+benefits+of+walking
 
Search terms for walking health research:
humans good at walking compared to other mamals
://www.google.com/search?hl=en&ie=ISO-8859-1&q=humans+good+at+walking+compared+to+other+mamals
 
I hope this research provides a satisfactory answer!

Thank you, this is perfect. Saved me many hours of research.

This looks like a great answer!

Walking is almost meaningless in freefall, so a variety of exersizes
were developed for the astronaughts to keep fit. Some of these would
be helpful for people with foot, leg, or hip problems that make
walking painful or impractical.   Neil