Second, theophylline has a different mechanism than caffeine. Both increase cardiac function, but caffeine has most of its impact on the central nervous system, whereas theophylline targets the respiratory system. For this reason, it is a common ingredient in asthma medications because it is a powerful bronchodilator.
To get a bit less specific... let me share my own experience. I noticed some changes in Jack3d's effect on me as soon as I bought my first refined batch last December. Overall I would have to say that the total amount of energy is the same, but now I experience more jitters. In other words, it seems like less of a "clean" energy boost, probably because more of the stimulant formula targets the CNS. And the change is most definitely not due to tolerance. I'm certain to leave 4 full weeks completely stim-free between cycles.
Anyhow, I do miss the old formula, but the new one for my money is still be best thing out there. Cheap, concise, mixes well, tastes good, overall a great product, which is why so many new preworkouts are pretty much just variations of the Jack3d formula.
Even if theophylline doesn't come back, I would still like to see another reformation in the near future. The arginine really doesn't belong... Ironically enough Gaspari sponsored a study comparing arginine to placebo and found that arginine makes absolutely no difference in muscle size, strength, and body fat over time. It really is an outdated ingredient. A while ago I criticized some for bragging about GPLC, and someone from primordial linked me to a study showing the clear benefits of GPLC. I would much rather see that in the formula than arginine, and I think most others would agree.