My wife and I are looking to purchase a piece of exercise equipment for our workout area in our house. Originally the idea was that we would get a treadmill, as that was something we could both use fairly easily. I've made no secret that I want a trainer for my bike (probably going to go with the Kurt Kinetic) but we can't really afford both at the same time... the trainer would have to wait for at least the winter. I was happy with this, as I probalby wouldn't want to use a trainer until that time. Unfortunately, all the treadmills we looked at which had all the features we were looking for would probably end up pushing that purchase to sometime in the winter, and then who knows when we would get the trainer. So, unless we settle for a cheaper treadmill or find a great deal on craig's list or ebay, if I want the trainer I'll have to convincer her that it would benefit us both.

My question is: how much of a pain is it to hook a bike up to a trainer? I have a road bike with 700c wheels, and she's got a hard tail mtb with 26" wheels -> would this require some extra step when switching between bikes that would make it more of a pain? Does anybody have any practical experience with switching out bikes on a trainer?

Haven't used a trainer myself, yet, but from what I've read, nothing but smooth tyres will work well, so you may end up having to get a second rear wheel, mount a slick tyre on it and put that on her bike every time.

However, one other option is to buy any cheap old road bike, give it a nice new rear tyre and have her use that. I assume you're too disparate in height for her to be able to use your bike - because with one trainer, only one person at a time will be able to use the trainer any way...

Actually, she's about 1 to 2 inches taller than me... not only that, but our porportions are quite different, she's mostly legs. We could probably make some adjustments to mine and get her to fit, but I''m very hesitant to do that.

I hadn't considered the rear whell problem though. I've wanted to get her a set of slicks for her mountain bike anyways, as she doesn't ride much, and when she does it's usually on a paved trail with me.

The trainers are designed to fit a range of bikes and to do it pretty easily. You adjust the width to account for any difference in width of the rear quick release axle and then you adjust for the difference in tire diameter. Typically the adjustments do not require tools and can be done in less than 10 minutes; sometimes much less.