Where can I get a good online file storage?

What would be the pros and cons of a file system that both allows items to be in multiple folders, and encourages this practice?

• I know that most modern file systems have such things as junctions and symbolic links (or whatever their respective terminologies are) to make files appear in multiple locations, but those aren't very commonly used, at least not by most popular software. The use of such a thing would open up a lot of capabilities, like for instance using a folder to sync to a cloud storage service like Dropbox, and adding items that aren't inside that folder.  (I know you can do that now with hard links and symbolic links and junctions, but I personally haven't had very good luck with that practice.) However it would also cause problems, like multiple programs having the ability (or thinking they have the ability) to delete a shared file. I feel like it would make organizational sense in many cases to have files in different locations, like for instance a team situation where one team member sees one folder structure and another team member, maybe a supervisor figure, sees a more broad folder structure, like a folder containing one specific file from each lower-ranking team member's files. Google Drive has an interesting file system where the actual address of each file (at least its URL) is not through folders, but based on a unique hash or ID which is a long string of characters.  Files are organized into folders, but this is just a way for the user to get to them.  If you move a file to a different folder, the URL of the file is unaffected.  Files can also be in multiple folders.

• Answer:

  Countless times I have had links to files in other folders, only to have those folders moved/removed and the files I needed completely lost.