I know there are quite a few threads on this already, some good and some bad, but I thought I would share my experience.
First of all, I have used the regular pre-workout supps namely SP250 and WF. I had some leftover WF I was using for a couple workouts before buying Jack3d today. Let me also state that I work in a 100 degree garage, 9 hours a day, 6 days a week and am fricken exhausted when I come home before going to work out at 10pm.
Now, WF works, but not like Jack3d. I only took 1 3/4 scoop to start off with (I am pretty tolerant to these things) and about 25-30 minutes later I could feel a strong focus almost like tunnel vision and I felt awake. Now, the difference between this and WF was that WF makes me feel super heart race pumped for a short while and then CRASH. WF also gives me a wicked case of shortness of breathe and little "focus" to take my mind off the day in the gym. Jack3d did just that. I felt awake and super focused.
On top of that, usually I end up taking long rests between sets as my mind drifts off but I was bustin' **** out non-stop tonight. It was awesome.
The price is a little steep for the servings you get but if it works this good all the time I think it is well worth it for me at least. I am jacked on Jack3d.
I'll keep you updated and see if this effectiveness tapers off.