It counts in my book!
Cooking Light ran an article (
Fluid Fundamentals) recently about how much water we should consume and their experts said that just about about any beverage and a lot of foods count towards your water intake. They counted a lot of stuff you wouldn't normally think would count, like soda, coffee, wine, and bread (yes, even bread has water in it and that water counts).
I imagine that plain water or water with a smidgen of fruit juice (such as a lemon wedge) is the best source of hydration but if that doesn't work for you (and it doesn't work for me), then I think Crystal Light is fine. I drink one 12 oz glass of plain water a day. The rest of the time I drink flavored beverages (Crystal Light, coffee, tea, fruit infused waters, etc.) and I'm able to stay very well hydrated on those beverages.