2G plus extras for people who sign up with you, PLUS heaps of aware apps at Dropbox
5G plus extras for people who sign up with you at Sugarsync, great for sharing
50G if you got on board at box.net at the right time, or 5G normally, and lots of collaboration/sharing opportuniy
25G if you were quick enough to claim it on your old Skydrive, and 7G if you were not.
I think, for once, Google has been behind the 8-Ball instead of in front of it. I'll take a look but I'm already using the four I've mentioned, and they suit me well.
Anything that I want on all my computers/devices. For example, I have a budget program which is dropbox aware, so I can store its database on dropbox. that means I can access the exact same database on my imac and on my MBP.
Another example. I have a truckload of ebooks, I keep them in a few places, so that I don't lose them.
I upload photos to it, and send a link to people that I want to give access to the photos. Or send them an invite to join that particular Dropbox folder. Much faster than burning photos to CD or emailing them.