Any luck getting summer campground reservations in popular National Parks?reservations

I have attempted and failed to make campground reservations for Yosemite Valley in the past (for the summer) and I'm wondering if there is anyone out there who has had luck with it?
Any luck with getting reservations for other National Parks that are popular? Zion, Bryce, Grand Canyon, Yellowstone, etc?
I'd love to hear any stories!

We had an easy time making reservations in Yellowstone LY for our RV trip in June. We decided to go as soon as the kids got out of school (actually we took them out 3 days early) so we could beat the crowds and made the reservation in February for 3 consecutive dates in Madison and 4 consecutive dates in Canyon during late June. We had no problem securing the reservations. We made the reservations as back ups in case we changed our minds when we got there and rearranged our itinerary. As it would happen we kept the reservations and were glad we did b/c the campgrounds filled up nightly.

I agree with meb123 Yellowstone comments. Several campgrounds are "first-come-first-serve" so we've discovered to just to show up at these campgrounds during check-out time. We usually end up with the best spots!

Also, as far as Utah's National Park campgrounds - if you can't reserve your spot during the high season, consider checking out some of Utah's state parks and national forest campgrounds that are near your destination. I believe you can camp anywhere on BLM land if you don't mind primitive camping - sometimes that's the best way to really see the stars at night.