I love dropbox. I have a CT who uses it and we all put our images in that one shared folder and the designer can grab from there.
I only use free dropbox, up to 2 gigs, so I have to clean mine out. There's a desktop application too which I do like a lot but I agree, be CAREFUL to only copy and not drag and drop. I have lost files by accident because I would just move them on over to dropbox thinking that the copy will be left on my computer (like if I were transferring to my EHD)... and then nope, it was moved completely. I learned quickly tho, lol. You can also use the online upload so if you are at like your work computer and you have a file you want to send to your home computer yet we all know email and stuff doesn't really work for some of those files, then you just login online and upload the file to dropbox and it's there when you get home. My mom also has access to mine so she can share photos and videos with me.