I just want to point out that spacemonkey (spacemonkey.com) handles this very elegantly.
spacemonkey was designed from the beginning to handle storing much more data than you'd ever be able to store on your laptop hard drive. The way it does this is it actually mounts itself as a FUSE filesystem and keeps it's own LRU cache of your spacemonkey data on the drive. If you access a recently created or accessed file it will just load from the disk cache. If it detects that you are running out of hard drive space it will automatically prune the stuff that hasn't been accessed in a while (so spacemonkey never causes you to have an "Out of disk space" error). you still see it though, it tells you its size, metadata etc. and if you try to open one of those files it will grab it from the network transparently behind the scene for you it just might add a little bit of latency (as if you were accessing something on a network share).
In 2014 you should not have to be thinking about what to "selectively sync" the service you use should just figure it out for you (and let you customize it if you need to)
disclamer: I used to work for spacemonkey but do not any more, although I think they make a great product and are a super smart team.
SpaceMonkey was recently acquired by Vivint, Inc. "The Space Monkey team is excited to announce that the company has been acquired by Vivint, Inc." I don't hold out any hope that SpaceMonkey as a product will continue on, or if this was more or less an acquihire.
Co-founder of Space Monkey here. I can assure you this was not an acquihire. At the highest levels of the org from CEO and down, Vivint believes in the Space Monkey vision. We're super excited to have their backing, and think you will be excited to see where this goes from here.
spacemonkey was designed from the beginning to handle storing much more data than you'd ever be able to store on your laptop hard drive. The way it does this is it actually mounts itself as a FUSE filesystem and keeps it's own LRU cache of your spacemonkey data on the drive. If you access a recently created or accessed file it will just load from the disk cache. If it detects that you are running out of hard drive space it will automatically prune the stuff that hasn't been accessed in a while (so spacemonkey never causes you to have an "Out of disk space" error). you still see it though, it tells you its size, metadata etc. and if you try to open one of those files it will grab it from the network transparently behind the scene for you it just might add a little bit of latency (as if you were accessing something on a network share).
In 2014 you should not have to be thinking about what to "selectively sync" the service you use should just figure it out for you (and let you customize it if you need to)
disclamer: I used to work for spacemonkey but do not any more, although I think they make a great product and are a super smart team.