I use DropBox a lot. I use it mostly to store some personal stuff that I might need access to while away, like a PDF copy of Nikon D90 user’s manual.
I also have started to use it to share photo shoots with customers. It is a great way to give access to mid-res copies of your JPGs for them to select from.
What I normally do is to post my pictures on DropBox right after my shoot. It is actually faster than burning a CD (or DVD) and my customers do not have to wait; they can download the pics when at home, make their selection at their own pace and get back to me with their faves.
If you are not familiar with DropBox, first get a free account here, then read this great post on DYI Photography. Great advanced workflow.