Stacking the fabric is sort of a pain, but as long as you keep your fabric pieces of a manageable size it's not too terrible. And if you're off by a thread it'll never show up - the nice thing about these quilts is that they are VERY forgiving - there is so much going on that if you get something a little off it'll never be noticed by anybody but you.
For me the worst part is pressing all the seams open. I HATE pressing seams open but for these you pretty much have to or you end up with a horrible lump in the middle. Otherwise I enjoyed watching it slowly come together.