Barefoot Interval training
I think you're probably right. I tend to have more TOFP when I'm running faster paces than slower ones. I haven't ramped up the distance yet since going bare for fear of TOFP and blisters. Five miles is the most I've gone and I did that fast. I'll just finish out my class (I paid for it) and then only do my fast runs for the class since that's just once a week and really concentrate on form on my other runs while decreasing my pace. Once I finish out my class- I'll start tacking on mileage slowly. I hope it doesn't take me a year to get back to my mileage and speed bare. Guess I'll just have to go with it regardless!
I found that with each speed increase, I had to aproach it like I was starting over, as if each speed increment required a different form. I'm sure it was just that each time I increased speed, my form went back to old bad habits (like over striding and pushing off), but I really had to focus to keep my form. My only issues were blisters though, never had TOFP until I did the ultra in VFFs. I really think TOFP is worse in minimal shoes than BF, but that is just a hunch.
I have found that Interval training / Hill Speed Work required a completely different method. In high school I was a sprinter. My events were 100 Meter and 100 Meter hurdles. All power came from the hips and legs and was transferred to the ground through the feet pushing off and driving into the ground with every ounce of energy. Barefoot, this would be a difficult task as it would shred the balls of the feet. Some form of protection is required.
Sprinting barefoot requires a much more refined approach. In my experiments I found that a gradual acceleration, straight and aligned body posture with the weight moving through the center of the body, forward knee thrusts engaging the hip flexors, solid arm swings with thrusting back motion, exaggerated lean from the ankles without a body lean and a very solid mid to forefoot plant followed immediately by a strong pull are essential. Any attempt to push off barefoot ends in hot spots and torn skin. Gravity is used to accelerate the body but to increase the speed, a forward drive of the knees and a strong swing of the arms can help increase acceleration without increasing the force exerted on the foot.
I like intervals on hills mainly for the added intensity but it also creates a situation where it is very hard to run in bad form. To climb a hill you need a high knee step and an exaggerated knee thrust as well as a forward lean from the ankles.
I included this picture because I love the alignment through the entire body. 
Now where did you find my picture!?
yeah i definitely like her alignment...that's some good alignment.
nice lavarunner. i'm pretty sure TJ didn't want you to post that one!
thanks for the advice. I went out this morning for my speed session and wore minimal shoes. it was much easier than last time. not sure if it was due to the shoes or the fact that i no longer have tofp. god bless that! i can tell now when i run that i am leading more with the hips. funny because someone here at brs had just mentioned that to me and i had intended to read more about it and just hadn't had time. then today- it just kind of naturally happened. progression, i suppose.
Wendy, for me personally, it was tougher on me to do intervals than long easy miles or moderate distance tempo runs. I was doing easy 8 milers regularly with no signs of wear on the feet. But when I would do 5 miles worth of intervals, I would get hotspots and some TOFP. I think it's both tougher on the skin, the tendons, muscles, and bones in the feet, especially when your still working on your form. Once my form improved, these too went away. Everyone's a little different, but this has proven very true for me.
No, it doesn't hurt!