I eat half a pack of fresh spinach everyday, I replaced it for regular salad leafs, havn't seen any bad effects so far.
. Personally I think you should listen to your body rather then reading up on something that MAY happen. If you were prone to stones, then reduce your intake. Untill you get them though don't sweat it.
I did have an attack of gallstones 5 years ago. Ouch! I never want to go through that again. I was told I could reduce the risks of getting them by lowering my fat intake. I do have a better diet now than then but I'm certainly not a saint when it comes to fat yet I havn't had another attack. But we'll see...