when i first started bike commuting to work 4 years ago, i was doing a folding bike/train multi-modal commute because i was not in good enough shape to bike 30 miles a day. i would take my folding bike with me on the train in morning, and then ride 15 miles home after work when i had all the time i needed to take it at my own pace. as the months went by, the pounds started coming off, and i started getting much stronger, so i began to eliminate the train ride some mornings and would just bike 15 miles each way. and after several more months of that, i had eliminated the train rides altogether and was just riding my bike both ways everyday. that's when i switched over to a regular diamond frame full-size bike.
but the folding bike did its job of allowing me to start bike commuting when the distances involved were just too great for me to do it all on the bike, and for that, my folding bike will always have a soft-spot in my heart.