All three of my kids have had one and it took a few days of getting used to it, but they all adjusted eventually. There was a lot of slurping! One food that they didn't really adjust to eating was lettuce. My DS doesn't really eat it, but my DDs do. They just avoided salads and lettuce on sandwiches for the 6 months or so that they wore the expanders.
If you are in the process of turning the expander, I HIGHLY recommend a lighted turner instead of the cheap generic one the orthodontist probably gave you. Our previous orthodontist gave us a lighted one (like a dental tool with a built in flashlight) and I, of course threw it away when we moved since two of the three kids had had expanders and I thought we were done. Nope! The current orthodontist had never seen the lighted tool, so I called the previous one to get the name of the company. Since I'm not a Provider, I had to order three or five, but the $25 it cost me saved TONS of aggravation! It is called the " AcuLight expansion scre key" from Great Lakes Orthodontics. Seriously, get one. (Or 5 since I believe that is the minimum order.). It will save you!