I've got:
25GB on skydrive (+7GB if I want on a second login) on hotmail - Supports the biggest file sizes iirc
50GB on box - free with hp touchpad - I'd argue the best web interface, just
5GB google drive - best integration with android on phone/nexus 7
2GB dropbox - it's the most cross platform so it's worth having just in case.
Home NAS which I can ftp or hopefully vpn into (new and untested) - the geeky approach to cloud storage lol
Google Music - will be full (yes 20,000 songs) when I sort it all out lol
Technically my webhosting has webdav too so I could use that if I wanted to....
What do I use... my NAS, skydrive and Google drive although neither skydrive or google drive use their apps. I use gladinet (windows) to map the remote storage as a drive on my pc so I can drag and drop without having to duplicate stuff a second time on each of my pc's. As to how much I use it... not that much if I'm honest, nas sees the most use as it's 'mine' and arguably more secure which is good for business storage. I do store things like fonts, things I might forget to backup before restore etc on skydrive which don't have any privacy concerns though.
Box very rarely gets used, I tried mapping a drive letter to it, which worked but it never automatically logged in and to be honest I just never seem to use it... same with dropbox although it is installed on my phone/tablet, like box, skydrive and google drive
Used to have ms mesh (remote desktop) installed but that's no longer being supported sadly so hoping the vpn I've set up will allow me to do remote network to home pc's if needed (rarely).