I was considering buy this kind of camera strap and after some reaserch i find this article
Karel
Interesting article about Camera Sling straps

Question to Canon.
There is an inquiry request for : EOS (SLR) Camera Systems , EOS
Digital SLR Cameras, EOS 7D
User Question : Hello, I recently purchased a shoulder strap for my 7D.
It is the type which can have a 1/4-20 stainless screw attached to it
... which can thread into the 1/4-20 thread on the bottom of the camera.
My concern is not the Stainless Steel screw..., but the solidness of the
thread insert in the camera itself, which (I believe) was primarily designed
to hold a camera, right side up, on top of a tripod. Is the screw insert solid
enough and secure enough inside the camera body so that it won't pull
out when the camera (and lens /70-200mm)is hanging upside down at my
hip as I walk around with it. Is there a maximum pull load rating on the
screw insert? Or,if you could confirm that it is more than solid enough
to handle all your pro DSLR's (hanging upside down with a 70-200mm
lens) it would prompt me to carry it upside down near my hip with the
shoulder strap. Thank you in advance for all your help. Sincerely. XXX

Response from Canon Technical Support

Dear xxx
Thank you for your inquiry. We value you as a Canon customer and
appreciate the opportunity to assist you. With regards to this
accessory there is no guarantee from Canon that it will properly hold
the camera in the position you mention.
Your notions regarding the 1/4" 20 thread on the bottom are correct,
this is for connection to a tripod for holding the camera right side up.
In this regard it is very strong and should have no problem holding the
camera. There is no published maximum load for this mount though and
for this reason I can't guarantee the cameras safety when mounted with
such a heavy lens being held down on your hip. The mount wasn't really
designed for this and damage may occur if this were to fall in this
position. We apologize for any inconvenience that this may cause you at
this time.
I hope this information is helpful to you. Please let us know if we can
be of any further assistance with your EOS 7D.
Thank you for choosing Canon.
Sincerely,
Technical Support Representative

Here is the response to same question from Nikon

Nikons response
"HI
Thanks for the question and sorry for the delay in responding.
The camera tripod mount is designed to support the weight of the
camera and lens but is not designed for potential shocks that this sort of
strap [using the tripod socket] may impart on it. In normal usage of this
sort of strap (sliding the camera up or down) it should be fine but we
would not recommend swinging or dropping the camera and having the
strap catch it. We don't publish any particular test data, though....
-David"
New Information (July 19, 2011):
At the recent New England Camera Club Council Conference in Amherst,
MA, Nikon staff were asked about attaching a sling style strap to the tripod socket.
We were told that the tripod socket is not designed to hang the
weight of a camera from it, and there would be serious concerns about the internal camera seals being loaded in a way they were not designed for.