Hi sammycakes,
I completed the 6-week rotation, and PACE Express was the only workout I used. It is designed to be your go-to workout, and I was thrilled with the time-saving concept.
Like slysam, I also lurked on the PACE forum and was disapppointed in the lack of activity there. Most of the posts dealt with the routine as described in Dr. Sears' book, and there were only a few that discussed the actual PACE Express workouts. Interestingly, I noticed that there was quite a bit of confusion surrounding how often to do PACE-style workouts. One of the posters even became quite miffed at Dr. Sears' lack of participation on the boards and his evading some rather interesting questions concerning "topping out" your heartrate. It seems like the forum is structured so the moderators take general questions to Dr. Sears, he answers them, then the moderators post his answers on the forum. Not a very close-knit atmosphere, that's for sure! And I think at one time, you had to actually pay to be able to access the forum.
I was happily going to continue PACE Express indefinitely, but unfortunately, I noticed that at the end of my first week of Round 2, I experienced some major overtraining symptoms, and one of the exercises injured my back. I'm thinking that since the original concept of PACE as Dr. Sears described in his book was only supposed to be doing the workouts at most 3 times a week, maybe doing PE 6 times a week was overdoing it, even with the short time per workout. I guess there's only so much intensity the body can take before it starts to fight back, which seems to be what I experienced. I'm taking it easy until my back heals, then I might go back to doing PE a few times a week rather than 6 times.
Looking at PACE as a 3-day-a-week activity, I think you definitely could do your own thing the other days of the week if you wish, as long as it didn't involve long cardio sessions. Leisurely walking or sporting activities would also work.
Hope this helps you!