What is an I/O

I've heard of inboards and outboards, but never an I/O

Can anyone tell me what an i/o is?

It's an inboard engine with an outboard drive. Another words, the engine is inside the hull, while the outdrive hangs off the back of the transom.

How good is there wake?

Better then an outboard, not as good as an inboard. This is generally speaking, the hull is what makes the biggest difference. I have an I/o

I like our boat because it's an I/O that has a good wake because it's a 26 foot deep-v boat, but if you like to hotrod around at speeds above 40 or 50, then it pays to have an outdrive rather than a v-drive or direct drive

Better fuel economy but way more expensive to repair.

Way more expensive to repair? I'd have to disagree, as the engines basically a chevy 4.3 which parts can be found at any car parts store. The outdrives may be kind of expensive to replace but a outdrive should last you very long as long as you keep it up.
Saying there way more expensive to place is pretty general if you ask me.

An I/O has far more prevenative maintanence expences than a DD,or a V drive.