You have a couple of options I think…
One is to purchase a NAS hard drive and plug it in your network - it’s as easy as it gets to set up a server. If you have gigabit ethernet or fast WiFi, it’s as fast as pulling files off a USB drive. I have a western digital and I can access it remotely in case someone needs a file too. I think you can sync it to the cloud but I’ve never done it
for full-on cloud storage, there are two I use that are pretty nice… SugarSync and AeroFS. Sugarsync costs $50 a year for 30GB - cheaper than DropBox and you can sync any folder, not just the one’s in the "dropbox’ folder… stuff like your "my music’ or “my pictures” folder
AeroFS another is another cloud/share folder but it doesn’t really store anything in the cloud, just on your different computers themselves. Because of that you get unlimited storage. You can access the files remotely and only have to worry about filling up your hard drive
Skydrive is cool but it seems like it’s more for mobile devices than computer share drives. Google Drive is the same in my mind. Dropbox is great but it’s expensive and you can only share one folder (the dropbox folder).