I have started several. Emphasis on "started". I did one here on this site sever years ago that I was successful with, Kept up and finished the quilt.
1. Pat Sloan - often just save the patterns for future use
2. Moda - save the patterns I like.
3. Edyta Sitar- never got past the materials list - I am working from stash and not buying special tools and fabric.
4." MysteryTrain" here on the Quilting Board. I have done several of them. Loved the results, nice size and pieces not to small and " fussy.
5. "Harriett's Journey" here on the Quilting Board. started, finished and the quilt is hanging in my dining room.
6. Civil War Quilts - Alcott Sampler - blocks finished but now in the UFO bin
7. Sew along by Quilt Police on the Quilting Board. - sampler blocks using 2.5" squares. Directions came once a week as I recall. Yes, I saved them to use again.
8.Wedding Dress Blue - a very simple RWB scrap quilt.
Yes, I do them. Would I do another, Yes, possibly. I will only do one sew-along at a time. I am personally not interested in something with thousands of tiny pieces. The end results are stunning, but I choose to use my quilting time differently.