I have a 5' x 3' Boos maple reversible worktop that's 2.25" thick. It has been warped since I received it from the factory. They told me to rub mineral oil into the concave side repeatedly and leave it wrapped in plastic until it flattens out. It has been over a year and I still have an eighty pound maple board in the middle of my kitchen, half-soaked in oil, wrapped in black plastic garbage bags. It has gone from about 5/16" warped in the middle to 1/8" warped in the middle, but I still can't use it for what I bought it for because it's warped. I bought it to roll out noodle dough, which is about 1/16" thick - so on a warped board they would be twice as thick in the middle as they are on the edges (or vice versa if I flipped it over).
Does anyone have a better method to flatten this thing out that doesn't involve a large planer? This has been one of the worst purchases I've ever made in my life, and certainly the worst cooking equipment purchase I've ever made. The first one was delivered cracked and I had to return it. It's not easy to return an 80 lb cutting board by UPS. Getting a new one took six weeks, which makes it a year and a half since I paid $500 for this thing and never been able to use it.
I should add that after I unwrapped it and left it out for two weeks it looks like it's reverted and warped back another 1/16" - losing my gains over the last month or so. I'm about to set it on fire and post the video on youtube with my story.