IMO they are a compromise. If you have room get a washer & a dryer. They usually have a lower load/capacity, and it takes a very long while for the dryer to dry clothes. In addition, you obviously can't wash a second load until you've dried the first! I had one 5 years ago & couldn't wait to get rid.
I love mine... Well, not "love it" love, but it does me. I'd go along with the space thing though - I reckon if I had the space, I'd probably go for two seperate machines.
It will do if you haven't got space for separates, but if you have, go for the two machines.
We had one in a previous (and small) house and found that we did a load of washing, then have to split it in two and dry it in two separate loads or it took forever.
We had a zanussi (cheap and cheerful) and it did the job, but like I said not perfect...
I wouldnt recommend one either. We bought one when we moved due to a small kitchen. The washers ok but you end up waiting hours for washing to dry in the dryer ... Save your money and go to Laundrette when needed thats what i do when im pushed.