Yes often. My mom sewed her entire life and one of her favorite sayings was "there's nothing as discouraging than a half finished garment". I usually go thru the following cycle:
Selecting pattern, fabric & making first block: wildly enthusiastic
Most of blocks done, but not set: what my mom said
Top completed: I guess it's OK, but did not fulfill my "artistic vision"
Quilted & bound: I LOVE it! (if I don't, there's always someone who will!)
I think I only have 1 UFO, although I have given a few away before the top was done...