I'm having very conflicting views on this right now. My first inclination was to put them really far apart to get that really wide soundstage. My speakers have good dispersion so the center fill has no issues with the speakers being far apart. However, I've been listening to many concerts this last two months sitting at the back of the hall on the average of 1-2 concerts a week. There is no appreciable soundstage width when sitting in row 50+. It's almost mono. So now I'm conflicted. If I put my speakers really close together, I'd more closely simulate my concert experience. Setting the speakers wider apart would simulate a much closer sound stage, I guess.
Of course, depending on the limitations of the speakers and your room/setup, you may not be able to place the speakers all that far apart before things start to fall apart.
Btw, the immedia site tips on focus and balance really helped. I found that listening to AM talk really helped pinpoint when the image was not in focus or smeared to the left or right, and also for balance, to check that the voice is coming from smack in the center.