The last I heard, there was no way for two people to use Wii Fit at the same time for, well, anything. I haven’t been able to find any options except for a 2 person run (which I wouldn’t use anyway.) That being said, I haven’t bought any system yet-- so are there any better options out there as far as 2 people being able to exercise at the same time rather than having to alternate? Thanks for all advice…
Dance Dance Revolution with 2 dance pads.
That would be good. 
But what I was kind of hoping to hear (well, read), was that some other system was an improvement as far as offering more 2-person fitness options of all different types. This may not even exist, but it’s always worth trying to find out…
Try the XBox Kinect. We just got it - and it has several games where 2 people compete side by side. There are no controllers to hold - it uses cameras to sense your body position and your avatar corresponds to your actions on screen.
I’m not sure of two person workout games available - but just the Kinect Adventures it comes with are quite a workout.
There are also dancing games where 2 people can dance against each other at the same time.
How’s the Kinect working out for you?
We tried it at a party and it was incredibly frustrating. One player or the other would randomly vanish from the camera’s sensors and it would take black magic to get him/her back in. We spent 1/3 of the time fighting the system rather than enjoying the game.
Incredibly well actually. But from what I’ve read you need to be careful which games you choose. Since it just launched some of the games don’t work nearly as well as others - read reviews and watch trailers on Amazon to get a feel if a particular game works and looks fun. There are only about 20 games so far.
As far as your problem with the Kinect seeing you - it might be either a calibration problem or else your friend didn’t have enough room for the Kinect (it needs a fair amount of clear floor space to work best). I’ve never had a problem with the sensor seeing two people - it works really slick. A second person can just walk into the floor space and the game automatically identifies that someone is there and splits the screen to let them start playing.
Well, there’s porn. 
Kinects been working out great for us too. Although I need to buy a bigger house. (Our rental has a small living room and we need to move the couch for really good 2 player action). We just have the Kinect adventures but there are also workout programs as well as the sports ones (volleyball, soccer, bowling, etc) that could give you a workout. My kids are flying all over the place.