Here's where I'm up to with my block 18 - it's currently sized 5 1/2" square. I just have the final round of half square triangles etc. to add all around the edge. It'll add another inch to the finished size of the block - and add 84 to the count of pieces in the block.
I had to pin the block to my ironing board to get it to sit flat as there are so many seams in the back. I can't even imagine what it will be like to quilt!
Really though, this block isn't hard as such - it's just really tedious, and I seem to remember Barbara having the same sentiment. Each row has so many pieces making up such a small section that they seem to take forever. And something I did notice is that in the line drawing, some of the triangles are facing the wrong way, even compared to the block the author made up. I've attempted to remedy this in my block.
Hopefully I'll have this block finished by the end of today - red and green half square triangles and yellow squares await!