MikeT - I took the spacer off a while ago. I think it was when I had some motor work done. Mossbarger made the reed spacer. Their phone is 800-891-1615. It was pretty cheap - around $23-$25. As far as what the spacer did - I never could tell you the big difference or if it was/wasn't a good mod. But for $25 - it was something to bolt on and try. :)
The V-Force actually looks to be a few mm's thicker than the stock reed block on the YZ 125 - so it acts as a smaller spacer.
Frito - about the jetting... first off we have never been able to completely get rid of a little low end bog on my bike - and we have tried EVERYTHING except for cutting the slide. I mean float height, pilots, air screw, clip position, main jet, idle, torque spacer, different plugs... everything! It is better now, though. I had the float height reset to 13.5 mm above the float bowl mating surface. I moved the clip position to 2nd from the top (3rd is stock) and could probably go to the top position, really. And I believe I'm running one leaner on the pilot jet which is a 22.5 (25 is stock on the '01 YZ). I adjust the air screw on a fairly regular basis (usually between 1 3/4 turns and 2 3/4 turns out). I have only rode twice with te V-Force (outside in upper 50's and inside in 70's) and it has been pretty awesome. There is a little bog when warming up the bike but not while riding. But we will hammer out the jetting even more when the season gets in full swing!