I've only vomited twice while doing any kind of training. The first was after I had passed the basic Navy Seal physical fitness test in Navy bootcamp(no I am not a navy seal and I did not go through the training). The second was after my boxing coach had me do 3 back to back 1 minute all out slugfests on the heavy bag. Those 2 made me puke. I have felt close to puking several times before, and just this last week I felt close to it, but it didn't happen. I don't think puking means anything really and I don't use it as a measuring stick for whether or not I worked hard in the gym. As for training so hard that you fee lcrappy the next day after or 2, well I feel that's really counter-productive. I used to train so frickin hard on just 1 set, that one set was a masochists nightmare kind of set, that it would take my CNS 8-9 days to recover from it. I used to think that was the way until after about 6 months of trianing I realized that I had gotten alot stronger, but my muscles weren't much more developed than when I started training that way. Lessons learned, you can train TOO hard, you can trian too little, and you can train too infrequently. I train myself to what I feel is enough, or hard enough.