I have to take exception to what bpape said. Yes, it's possible to get reflections, depending upon your room acoustics and how your speakers are positioned. And yes, it's possible that the imaging may be reduced. But these are not foregone conclusions. As I said before, I have my bookshelf speakers in my wall unit entertainment center. My speakers (Paradigm Reference Studio 20's which are front ported) image as well, if not better, than the 20's did in the three stores where I auditioned them. It can be done.
In the world of electronics, there are some, purists, who are absolutely uncompromising in their quest for audio nirvana. Nothing will get in their way of achieving the "perfect sound." Not that there's anything wrong with that. However, for most of the rest of us, compromises are the norm. We like perfect sound too, but it's not the end of the world if we only get excellent or very good sound. For us, there are other considerations -- money, aesthetics, room configurations, WAF, etc.
My suggestion is to find a dealer who will let you audition them in your home after your wall unit is built -- just to be sure that you get the sound you're looking for. Remember, position them so the front baffles are forward of the edge of whatever they're resting on. Ensure the tweeters are at ear level. Experiment with "aiming" them; in most cases, they sound better when they're toed in slightly so that they're aimed at the listening position.