Amazon has really been bad lately it seems, with toys/collectibles in particular. Almost every item, Star Wars or otherwise, that I have pre-ordered or watched over the past few months has been continually pushed back until I eventually find it elsewhere and cancel it. I still use the Amazon preorder as a form of "fail safe" if I can't find it elsewhere, but it ends up being delayed so long that I find it somewhere else first. Like Jesse mentioned, I hated to do it, but when WM.com had the Clone and Sith Evo sets in stock, I ordered them. Got the clone one in a couple of days, and the Sith one should be here early next week.
I've preordered and cancelled the Evo sets, 500th Vader, Unleashed, etc. all from Amazon, and they still haven't had them in stock since then. I currently have some of Marvel Legends 10 preordered there, but I'm quite certain that will never come through either. The shipping date kept getting pushed back and pushed back on their listings, and then yesterday it now just says "items is not available". Always a good sign. I'm hoping those turn up at retail soon too. I've always had great luck with books and DVDs from Amazon, but the collectibles area has really been bad this year.