I've made this pattern several times and didn't have too much trouble with it. My measurements are larger than the largest size 18, but I got it to fit by reducing the seam allowance to 3/8". I made the dress as well, but actually had to take it in more because it felt too big. I was able to take it in about 2 inches!
I generally only use pattern sizes as a guide and usually sew the pattern with cheap fabric the first time around. After I adjust the fit, I draw my own pattern out of freezer paper and mark the changes I made on the pattern's instruction pages. This way, I have a pattern to use that fits and can be ironed on over and over again. (I don't have any patience for pinning.)
As for the neck, I don't remember having any issues with that except that I used way more elastic than they called for because I wanted my neck larger and not as gathered.
Here's the link to one of the shirts:
http://www.flickr.com/photos/7791990@N04/731481191/And the dress:
http://www.flickr.com/photos/7791990@N04/2437473532/There's alot more examples of this pattern on flickr. You could do a search and probably get more info on what other's thought as well.