Is it true that fluoride is really good for your teeth?

Yes,works 4 ways. 1) when Fluoride is incorporated into the tooth's enamel it makes it harder for the enamel to lose minerals when exposed to an acid challenge. 2) when Fluoride is in the saliva it makes it easier for the enamel to pick back up minerals that it has lost. 3) Fluoride inhibits the oral bacteria's ability to produce acid. 4) Fluoride inhibits the oral bacteria ability to stick to the teeth.
Yes. Before carefully controlled Fluoride programs people were ear to ear silver fillings to fix mouths full of cavities. Fluorides and sealants have reduced new cavities in children by over 90%. Fluoride has saved untold suffering in children. At about 35 cents per person per year it's amazingly inexpensive.
Definitely, yes. There are many scientific studies done by research scientists which indicate a variety of dental benefits associated with fluoride and fluoridation.