Cloud services are great for what they are. I use Google's daily and frequently find myself rummaging through a Dropbox, whether it's my own or someone else's.
But boy, are there limitations. I often work in the subway while on my way to somewhere else, and Google's docs just aren't an option there. Sometimes I need to shuffle large collections of files—an excruciatingly slow upload speed could make it a slog, and many services require a monthly fee for storing them. Most experience sporadic outages, and a few have gone away entirely when their initial funding ran out.