At least thee years ago Microsoft setup an online file storage system called SkyDrive which has been very much under utilized all of these years. It is about to under go a significant upgrade that will make it much more useful with the release this summer of Windows 8.
Before you stop reading this realized that SkyDrive can be used with the MAC, which would include all of the current iOSs and Windows 7. SkyDrive may prove to be a significant tool in the near future with applications available for the Android devices as well as the iOS devices.
The neat thing for most users is that the cost for 25 gigs of storage is FREE, which you'd have to admit is pretty cheap. The only restriction that I have found is that you are limited to any give files size of 300 megabytes, which in most cases isn't much of a limitation at all.
The current version is web based and does not give you a drive to interact with off of your computer via either the desktop or from within an application much like Drop Box does. But this will change with the release of Window 8 in a few months. This capability will come to Windows 7 as well.
It was originally designed as a collaborative way of sharing files in a group and it has not lost any of that ability. You can even share files via a browser link with people that do not have a SkyDrive account.
It costs nothing and gives you 25 gigs of free storage and has a very simple interface, how can you go wrong especially with the upcoming update? Give it a whirl and see what you think.