Like the others have said, it's personal preference. I personally would never do it again. I've had a few over the years (mostly as a tenant) , so like most rental houses/apartments a lot of major appliances are older or heavily used. They are not a fun set to deal with when a repair man comes in, or to have half of it replaced.

Also you need to take into consideration that if your buying a specific stacked set, the washer basin for example, is often smaller than one in a conventional, so if you have large coveralls or bedding to wash often, it may not be as practical.

If they are the newer front load models, you won't have to worry about the repairs for awhile (knock on wood), but you should consider anchoring the dryer somehow. Just for safety, in case of things like earthquakes etc.

AND MOST IMPORTANT OF ALL consider the weight displacement and how good things like your subfloor is. I had a landlord who's contractor assured him that the floor would be fine if he stacked the dryer on the washer. That calculation wasn't including the extra weight of water and clothing. The vibrations, extra weight etc made the floor bow in a scary way after awhile.

Hope this helps!