Yeah, a lot of us have had similar thoughts of using various forms of free storage like our own hard drives and RAID setups.
This should just go toward reinforcing our understanding that ideas are the easy part. Follow-through is the hard part.
Time was Google providing "unlimited" gmail storage and fuse gmail-fs was just released. I looked for another fuse fs like a hotmail-fs but did not push hard on it. I could not find and let my idea die.
It was hard to do and time consuming, but marginal gain would be small. Also I'm a f lazy system administrator. I hate coding :)