I'll bump this up by saying that in my last house the corridor kitchen was too wide to be an efficient galley and didn't have any space for a permanent island. It was a rental so I just used an inexpensive wood topped, counter height cart with wire shelves. It was great. It was always in the way, to a certain extent, because the sink was across from everything else, but I could push it in front of the oven, or push it against the counter return, and just not have to deal with it when I didn't want to. It was a perfect intermediate landing space, and prep area for the stove (which had hardly any counter by it.

My mother has cabinet on castors with drop leaves in her dining room. When not in use it's a small sideboard with a decorative bowl on it, and serving pieces inside. For entertaining it wheels up to the table when it's set as a buffet, or into the entry or living room, or into the family room where banquet tables are set up for crowds, and has variously been a wine bar, plates holder, carving station, coffee service, or desert display.

I'd say that the biggest questions to ask yourself is where the island will be, where it will go when it moves, what you want to use it for, and what it will be blocking in its various positions.

A similar question was recently asked in this thread.