Funny I am currently working on a t shirts quilt for my DD, I used interfacing, and I have so many different size blocks my head was spinning. It has taken me 3 full days to work this out and that's after I had ironed the interfacing on. Soccertxi your quilt is beautiful mine is.........well not beautiful but it's what she wants. She also wants it fluffy and tied not quilted so that is what she will get. I have two more sets of shirts to sew on and the top is done. I'll have to make one more for my other DD but I think I'll give it some time this one was a pain in my patootie!
Good luck Barking Rabbit I used about 60 shirts going all the back to kinndergarten all the way to her graduation from college. It's kind of a hot mess but she will love it.