My miracle berries arrived today. The berries themselves have a very mildly sweet flavor, but what they're known for is for making anything else taste sweet for around 30 minutes after you eat them. I ate a whole lemon with the miracle berries and, while the miracle berries did sweeten the flavor of the lemon, there was one thing that I didn't take into account: miracle berries are not going to do Jack shit about the extremely high acidity of lemons. So, while I did eat the whole lemon (and it was a BIG lemon), it still hurt to eat and my mouth is now burned and stinging badly. It would have been even worse if I had drank lemon juice or lime juice like I've heard about people doing with miracle berries.
I need to find some sour foods that don't hurt your mouth and try those with the miracle berries. I put the rest of the miracle berries in the freezer for now.