There are two thoughts on (I assume wall mounted based on your picture?) speaker placement. 1) center the speakers w/ regards to the TV 2) high enough that the tweeter is located at ear level when you are sitting in your viewing spot.
For surrounds, it is usually common to mount them so that they are higher than ear level by at least a foot or two, but I am sure you can find all sorts of opinions based on bi/dipole direct radiating, etc. Checkout dolby's website for some general speaker layout suggestions, including angles from the TV.
Also, if you are going to run the speaker wires in the wall, it's best to use CL2 rated wire and not "regular" speaker wire.
Also, if the notion of snaking new wires to the TV at a later date would be quite difficult, it would be good to just run a nice fat conduit to the TV location when you eventually need to replace the HDMI cables... ...after all, the replacement for HDMI is already starting to be added to products.