It's not the number of calories alone that is considered going 'very low.' You have to take into account your height and age. There are so many online calculators that figure your resting metabolism rate (here on fitday, there's one, I think...) To even consider 'starvation mode,' you have to know the number of calories your body needs to begin with.
That said, I don't believe the 'starvation mode' stuff either. I can't find any studies that mention 'starvation mode' - although it's not hard to find a blog that mentions it. I think that whole thing is kind of sketchy. When you lose weight, your metabolism adjusts downward just because you have fewer pounds on your frame to maintain. But it's so slight an adjustment over time that it's never going to count as 'starvation mode.'