I'm just curious if most of you do the same cardio circut for awhile and then switch to something new as your body adjusts? Or, do you do different types of cardio each day? Is one way better than the other?

The last - and only - time I lost quite a bit of weight was 7 years ago and I did basically the same cardio routine for months at a time before changing my routine. This time around, my whole lifestyle has changed. I've gone from being single and "carefree" (staying at the gym for hours on end... ...heck, I even met my DH there!) to busy, full-time Mom to 2 small girls. I do some form of cardio every day - and lots of it - whether it is on the StairMaster, elliptical and treadmill at the gym, or walking outside (which involves pushing a BIG double stroller!) or an exercise dvd at home. But I rarely do the same form of cardio 2 days in a row. I'm losing an normal amount of weight, lots of inches and feel great. I like the variety. I just don't know if there's a "science" behind having a set routine or if the magic is just in moving my body?

Change it up. Your muscles/body adapt to the same movement within a 2 week period and results taper off b/c of that. Muscle confusion created by changing your routine be it cardio or weight training keeps the muscles/body in a place where they can't predict the next movement therefore they can't adapt to the movement.
The only thing i can think of that might vary on this is walking on a treadmill, simply b/c after a week or 2 you should be able to add an incline whichi will target more of the back of the legs & glutes, and also increasing your speed as well as time or a combo of 2 or 3 of these. There are ways to constantly change a routine, you just gotta get out of the comfort zone and do it sometimes.

I try to do two or three different things each week. I might walk two days, do step aerobics two days, and Gazelle or exercycle one day. I don't follow a set routine, I just try to do something a little different than I did the day before. It seems to work for me.

I do the elliptical, bike, pilates class and a cardio seduction class each week. I also do strength and weight training as well.

"They" say changing things up is the best way to go. If you have been having a harder time losing maybe you should try to go higher intensity and doing interval training? I have been having a lot of luck with this. I have been using cardio coach to learn more about it and get me through it.http://www.cardiocoach.com/

I think mixing it up is good because it helps you not become too bored.
I normally work out on the elliptical machine or the treadmill, but, I recently started this bodypump class at the YWCA. I am planning on taking water aerobics this summer.

Even if its just changing the order you do things. So instead of doing treadmill, bike, x trainer, stepper, rower every day, constantly mix it up. Do higher intensity if you can. Higher levels on the bikes, different incline, different speeds. I always set myself a goal (whether it be 90 RPM on the bike, 30SPM on rower, or 7.0 on the x trainer) and when I can do that easily for the full time on it, it goes up a level.

Most of my cardio is running (I do some weights, yoga and swimming too), and I don't actually change to other types of cardio - I just change the way I run. I do short fast runs, long slow runs, speed intervals and hills to mix it up a bit. I never do the same run twice exactly the same!