I voted no.
In RO, it would simply be too impracticle. Even if the thrower hasn't cooked it off for a second, or two (which would be rather silly on their part), depending on how far it was thrown, you're looking at it being cooked a maximum three seconds and a mininum one, just in flight time. Then by the time you reach it, unless you're lucky, or unlucky depending on your viewpoint, and it lands at your feet, you're looking at another second gone. Well, just in that alone most grenades would have gone off.
If you're stupidly lucky, and get a grenade with a full five second fuse (I havn't been that lucky thus far, but who knows) you've got another two seconds to pick it up, and find someplace safe to throw it. You've also got to throw it a decent distance, or else you'll still be killed, or at least take damage.
If you're as lucky as me though, you'll get a grenade with a three second fuse that blows up the second it touches the ground.
For those people that have stated that it's effective in DoD, yes, it is. But again, only if you're dealing with people who havn't figured out that whole "Cooking" fuction in Source, and who hadn't figured out that you can drop them, and pick them up in 3.1 and earlier. I've personally played DoD for four years, and I've never been able to actually pick up a grenade and throw it back. Picked up grenades before, yes, but only to have them blow up in the face anyways.
For the "BUT ZOMG!! DOE'S GUYS IN SPR PICKED UP DEM NADEZ AND CHUNKED THEM BACK!" arguement, that's inane. Load up SPR and go to that scene. Count the time that it takes for the grenades to explode from the point that it leaves their hands. Just did it myself, I counted 6 seconds very, very slowly, and 7-8 seconds at what I thought was closer to a realistic second count. Now, go into RO, toss a grenade at your feet, without cooking it, and count how many seconds go by til you get evaporated into a fine red mist. Is it 6-8 seconds? Hell no.
Either way, should the Devs include the option? Sure, why not. Can't be much more coding to pick up a live grenade than to pick up a fallen weapon. And then you all can go and try to pick up grenades, and I'll just run away when I see a grenade coming at me. We'll see who survives more often.