If you can leave at 30 weeks, then go for it! It is absolutely a personal choice.
DH is happy for me to go at 28 weeks, which we discussed before TTC, but now that I'm at a desk job I could probably stretch it out. I'll be 36 weeks at the start of our Christmas break, so that's when work will want me to go. I get the feeling I'll want to go a bit earlier, but we'll just see what happens.
My predecessor worked up til 37 weeks, and did a really bad job of the last 4 or so, and was stressed out of her pants. I don't want that to be me.