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.

Depending on the quality of your main speakers and their ability to image, a phantom center can be a better alternative to an actual speaker. Although the dialog won't be as "anchored" for those on the sides, integrating a center channel speaker (for music) can be quite challenging (much like integrating subwoofers).

I used to have an actual center channel. I currently use a phantom center and find that the image is much more cohesive this way.