phantom center channel

Yes, it can drastically change the experience - many times for the better. I often experiment turning it on and off to see which sounds better. DVD concerts are almost a no-brainer for turning it off.
Remember that a center channel's main purpose is to anchor the dialogue in the center for those who are off center. Depending on where your seating position is, it may not be a necessity.
For a long dissertation on not using a center, go to Richard Hardesty's Audio Perfectionist website.

I agree with the above. I'm currently not using a center channel and it's working very well, and I don't have to physically have a speaker in between my mains. If it is for one or 2 people you can get away very well with a phantom center--and often times it's actually an improvement.

Snofun3 is correct, for movies. If multichannel music is the objective the center front channel is the most important of all.