Placing the speaker near a wall will alter the bass response no matter where the port is at (or even if it has a port). That said, I've had speakers right next to the wall, rear-ported units just a couple inches from the wall, and even rear-ported units smack up against a support column.
With the exception of the last case (they were placed for simple ambiance in a temporary setup), I can't say that the general signature or "sound" of the units was noticeably changed. They sounded good no matter what. I'm sure they would sound even better when placed properly, which is something that has to take into account the entire room as well as the speakers themselves, not just wall proximity or porting.
While I'm not a guru on it, I'd feel comfy with a foot between the back wall and the port, and somewhat more than that between the speakers and the side walls. But in my experience it's not the end of the world even if they aren't.