Symlinks seem to be more popular - people use them e.g. when moving installed games from one disk to another. I've been using them for years. Tried them with uTorrent a few years ago - and it didn't work, apparently because it's adding ".!ut" to incomplete files, and it breaks the link. Only now I tried hard links - and it works. And with DupeGuru you can even remove duplicates from overlapping packs, but still keep seeding them all, thanks to hard links.
D