Jeremy asked someone to start a thread about OwnCloud, so here I am!
I’ve used owncloud pretty much since it was first released, as I’ve always been of the opinion that relying on someone else to sync your data is a terrible idea.
As a web application, it’s not bad. However, the plugins (“apps”, adding stuff like calendaring, ampache media streaming etc) tend to be of dubious quality. There used to be a lot included by default, but in more recent versions it was stripped down to a bare minimum with most being optional. As a way of having a web interface to your files and allowing you to share them (either with other users, or with anonymous public links), it’s a great tool.
However, the implementation of the syncing is poor. If you try and use it for more than a couple of GB of files (e.g., my music collection), it falls over completely and fails to sync. When it does work, it’ll occasionally get confused and create a copy of every single file with “conflict” appended to the file name. For this reason I actually use BTSync (considering switching to SyncThing) for file sync and just use OwnCloud for the web interface.
Version 6 added OwnCloud Documents which is a promising alternative for collaborative editing a la Google docs. My first experiences of it were that I could successfully share a link to a document and collaboratively edit it… once. I need to re-visit it now it’s a couple of months later and see if this has improved.
In general, OwnCloud isn’t all bad, but it’s not the one-stop “self-hosted cloud” solution that it intends to be.