Sippy Cups

Anyone started sippy cups yet or plan on it soon? I've read that they should start around 6 months, but could start at 4 months if they take to it well. I've also read not to put formula in their sippy cups for some reason? Aren't they supposed to be weaned off of bottles as soon as possible for dental reasons? So my logic would be to just use a sippy cup instead of bottle at feedings as soon as they will drink from it, then transition to straws and regular cups as soon as they will drink from them.