In wall vs regular speakers?

I agree with some of the other posters but allow me to share my experience:  
I have a tower 2.1/5.1system consisting of B&W 802's, HTM-1 center channel and CWM-DS8 in-wall surrounds, and ASW-800 subwoofer.  Another 5.1 system consisting of Klipsch R-5800-W (L,C,R), R-5650-S in-walls, and RT-12D subwoofer.  Also B&W CWM-8180's in-walls in a second zone for two channel only.

With the two systems for 5.1, I can honestly say that I could easily be satisfied with either (don't tell my wife) on 5.1 material.  Of course with two-channel the 802's are in another stratosphere.  But in both systems the quality of amp/pre-amp, or receiver approach plays a huge role in bringing out solid 2-channel performance.  I'd say in both cases separates is the way to go, but in the 5.1 Klipsch system using a quality receiver is quite adequate.

With the B&W 8180 two-channel system using a Vincent SV-236-MK2 intergrated I would say aspects of depth and presence are there... Just not at the level of the 802's, but very satisfying.  Coincidently before the 8180's were installed I used Klipsch R-5800-W's with very close results.

Sorry I guess I should have specified that the question was for the surround and back speakers only as I already have a stereo setup that I will be implementing with the HT, thats what I currently have, both receiver and pre amp are connected to the same amp although be it through the same pre amp, my pre does not have a pass through so I just set it to 12 when ever i switch to HT input.

So the system will be used for both stereo and ht, as far as my setup is concerned I am very happy with my front, I have Rethm Saadhanas for mains and Audiozen pre and amp and Lumin T1 for digital.  For HT i am using Marantz, currently my surrounds are paradigm v7s, my ceiling will be monitor audio CT 280. Its the surrounds that I was thinking of changing mainly for aesthetics but I believe the general thought is that in walls are worse than regular speakers, if I understand correctly.

In my case the in-walls that I’m using fire in both directions in dipolar configuration, and have a very wide dispersion of sound... Even in the case where one room has an open side to an ajacent room. For the enclosed room side placement is just as effective as rear only install. Stereo center imaging is a touch more pronounced with the rear install, but both placements acheive outstanding full/ambient surround.

I initially had on-walls in both setups but for space, or a more stealth-WAF decided to try in-wall in the open room. Then once I heard the performance and felt I was missing absolutely nothing, decided to switch in my main listening area. Honestly can’t comment on monopole designs as I’ve never used them.

A buddy of mine had tower fronts and in-ceiling surrounds, and I thought it worked surprisingly well.  The rear speakers being behind the listening positions produced a nice, diffuse surround sound that created a very seamless and immersive experience.  That's what I'd do if I was creating a home theater since it worked so well, with the obvious added benefit that the speakers were completely out of the way and basically invisible. If you're thinking of getting seriously into surround music I'd probably use traditional box speakers. 

Sounds like you don't use a center channel speaker?

I do, I forgot to mention that I have just ordered a matching Rethm center, should be here next week, looking forward to it.  Before that I used a paradigm center.

Although I can say that spending a week or 2 now without a center, I can honestly say that the two fronts are doing a good job at mimicking it.