I did the 30 Day Shred workout program in June, 2011, and found it to be a great way to start each day (I have a review of the 30 Day Shred on its page). I kept using it until I finally received "Ripped in 30" at my door in August.
There are definitely a lot of similarities between the two programs: they both use the 3-2-1 system - 3 circuits of 3 minutes of strength, 2 minutes of cardio and 1 minute of abs, with a 2 minute warm up and cool down. There are beginner versions of some of the tougher exercises.
What's different? Well, the videos are longer on average, so if you're working out in a limited space of time, you may want to allow about 33-38 minutes for each video. Also, there are 4 different workouts instead of 3 in the 30 Day Shred.
The exercises do not repeat at all over the 4 workouts, and I believe that weeks 3 & 4 are a bit more advanced than the 30 Day Shred. There are a lot more exercises in this program that develop balance and coordination. Jillian pulls from her experience in martial arts to bring some rather intense moves.
Jillian incorporates a lot more motivational talk and constantly reminds us that it's more than just about exercise, but about bringing our A game and stepping up every day of our lives.
The main complaint I had about the 30 day shred was the several minutes of messages that you have to wait for when loading the DVD. Thankfully, in "Ripped in 30", you can now skip or fast forward through the messages to get to the workouts quickly.
Overall, I believe this is a good program for intermediate to advanced training. If you're a beginner, you could stay on week 1 and 2 videos much longer to build up your strength, stamina, balance and coordination. I consider myself intermediate level, and still have trouble doing the advanced version of many of the moves. This program will definitely challenge you.