Yes and no. I went through two 4-week blocks of QD a couple years back. The fourth weeks I did a substantial "back-off" where I hit the gym for two light full-body sessions. Believe me, after 3 weeks of QD you'll need to back off the weights for a while.
To be honest, it felt great! My muscles didn't ache or burn...and I didn't feel run-down leaving the gym...the explosive day is refreshing and mentally recharging.
Nothing major. I think I ended up substituting a few exercises...I haven't looked at the program in a long time but I do remember tweaking it slightly.
The repetition day (2nd day I think) is a bitch...I'm in pretty good cardiovascular shape but it had me struggling for air...plus by rep 15 or 20 your muscles are burning and your body is shaking. If you're looking at the program thinking "oh, that's the light weight day, it should be easy" don't.
I'd be interested to hear your feedback.