Microsoft had built in cloud storage, something like live space, or live disk, or something along those lines. It was very similar to dropbox, but for whatever reason it didn't catch on. I know a few people that still use it.
That's the thing - Apple and Microsoft have both had somewhat similar offerings, but in some way they were not as user-friendly, or were not presented to users properly (Apple has iDisk, or something like that).
For LAN use, cloud (external) storage isn't even needed though.
I get the feeling that Apple is preparing another big push into this area. Between cloud-iTunes, the mega datacenter, and rumors of some sort of new iPad sync system they've got plans for sure.
the reason it didn't catch on is because it was terrible to work with. it did not synchronize consistently. it would detect that changes had been made in multiple locations, then just keep extra copies -- leaving the user wondering why the number of files suddenly exploded. I used it for a bit, and finally gave up because it was too much hassle.
