I always shot my D 50 in JPEG, and view it on Windows 7/Picasa. My monitor is calibrated as close as I can come, which appears pretty close, and when I try sharpening from Picasa, I can't tell much about it, except when the levels get nearly maximum, the image goes all wonky, looking like a bad HDR!
Actually, even after I found out there was this digital thing called sharpening, which previously was something I only did to my hunting knives, and my wife's kitchen knives, I seldom observed what I thought was the need for any additional sharpening in my images.
But, in the True Spirit of Never Leaving Well Enough Alone, I started reading,(I'm a photographer,right?)and thought; "Hmmm...I wonder if there is something I am missing?"
The jury is still out. My buddy, the Canon shooter, sharpens the merrie Aitch out of his, but I really can't tell much difference between his'n and mine, except mine are better!
I have bought a D90, and found Ken Rockwell's site, where he has a D90 user's guide, so I set it at his recommendation, where it will stay, until I think it will be an advantage to change, if ever.