My experience with this strap has been very positive.
Not long before I got this strap, I had a grueling 13 hour photoshoot for a wedding, starting with the bride and maids at the hairdressers and leaving half an hour before midnight. During this time, I had my D300, SB600 mounted a Fong-like sphere attached, hanging from my neck.
The day after, I felt like I had competed in a K1 tournament in Japan - principally my neck and back.
After attaching this strap, I had a 6 hour birthday shoot and felt nothing. Very pleasant and the wide part/the cushion has some give in it, so vibrations are softer, instead of transferring as jolts.
I can warmly recommend this strap for any extended shooting/walking around sessions.
When I shoot my D40 with the 35mm AF-S, it's not exactly needed though and may even seem a little too bulky, comparatively speaking. But for anything D70/80/90-sized and up, I'd put one on.