I was told never to buy a washer/dryer because there is one motor doing the job of two appliances, so it would last a far shorter time before breaking down. I ended up buying a small dryer because I didn't want to be without, and because I use the line aswell. It does the job perfectly, and takes up less space.
Have you thought about what you'd be washing? I find that it's extremely rare that a whole load would be suitable for the dryer anyway. There's always something that shouldn't be tumbled, and you wouldn't be able to fish that thing out so easily!!
Wasn't there also a big scare about how hot the washer/dryer doors got a few years back? (Quite a few years probably - I am an old fart after all...)