I've just removed my FCE, as my GIPro gear indicator stopped working when I installed it, and a subsequent installation of an MC Cruise wouldn't work with the clutch wired connected. The clutch switch was tested ok, and then swapped out with a known working switch, but the problem was still there. As the first problem only occurred when I installed the FCE, I thought I'd remove it to see if it fixed the GIPro problem, and it did. Gear indicator worked immediately. I then plugged in my MC Cruise clutch wire, and the MCCruise is now working as it should. It did work fine without the clutch switch connected, but it wouldn't work at all connected to the clutch switch with the FCE installed.
Overall, I'm happy that the problems with the clutch switch have been sorted, and I'd have to say that removing the FCE hasn't had a negative effect on the throttle response at all. The FCE I have was installed on an 03 model I had but wrote off. I bought the wreck, as it was only superficial damage, and the engine ran fine. On the 03 bike, the FCE had a positive effect, but only marginal at best, and fuel consumption increased on it as well. The 08 model wasn't as snatchy as the 03, but I thought I may as well install the FCE in it anyway, and doing so, the improvement was only slight, if at all.
My FCE is now a paperweight to me, and not a good one. IT didn't really work well for either of my ST's, but I'm sure, as has been shown in this thread, that it may work for another ST out there.