That's too bad. I was in Seattle for a convention (work) in June, and found Pronto a really great way to get around. As an out-of-towner, it also allowed me access to parts of the city that I otherwise might not have explored.
That said, I can see why there might be challenges. It wasn't quite clear how to get a helmet (I travel with one, but most don't). And the Pronto bikes were quite heavy - good for flat terrain, but a bit of a challenge pedaling up Cap Hill and to UW.