I used it once upon a time when I did a lot of file transfers from school. I don't really do many anymore, and I get unlimited Google Drive via Google Apps for Education, so no need, but it worked well enough. I think I used 9.0, but I don't remember for sure. I never really had any big bugs with it other than some server permissions issues.
I have a instance of owncloud running... 99% only for small file syncing... despite my best effort it feels like a snail, chained to a rock, that is stuck under a even bigger rock ... i guess you get it.
All other sites on the same machine, no mather what wired framework (joomly or wordpress) feel snappy and all.. but owncloud ever since felt snaily.
Yeah the server is in a datacenter... not local! And I would never, ever, ever trust owncloud with sensitive (a.k.a. not pre encrypted stuff) or contacts.. as google got them anyway.. so they are public domain :P
As for using OCL 9.. i am on 8.2.2 (stable) and dare you I will not touch that unless a security update comes... for as long as its not EOL
I have listened to an interview with one of the owncloud peeps and it seems to be moving in a direction I like. I have not had a chance to move to 9 from 8.2 but I will soon.
8.2 actually met 90% of what I wanted. I run my own instance to play with and it keeps my note's synced and files synced. I've been using it for at least a few months. I've not had any trouble with it and am pretty happy with how easy it is to use once setup. I don't think it'll satisfy advanced users though but it's doing what I want it to do and it's doing it well.
I did it again... i read the changelog and found the improovements on security worth upgrading. And now the code integrety dives me nuts ^^
I have a modified .htaccess so that LetsEncrypt will work as well, of course the .well-known folder with its own .htaccess file. And of course, the code signing .jason thing now complains about the modified .htaccess in the / and the .well-known folder the .user.ini from php and the .htaccess inside .well-known;
And once again, the owncloud documentation is deffinitely no help at all.
I run OwnCloud 9 on Ubuntu 16.10 Server in a VM at my house, and after a few tinkering with PHP settings for a while, and installing Let'sEncrypt, I have a very speedy Dropbox replacement that so far has worked remarkably well. I have to warn you, however, not to, under any circumstances enable the clamav plugin. It sucks CPU like nothing I have ever seen and slows transfers to a crawl sitting at near 100% utilization all the time. If you want AV then set it up outside OwnCloud to scan periodically. I also love how it integrates decently with Active Directory or any other LDAP server. If you do decide to set it up, to get it usable for transfers bigger than 2MB (the max for default PHP7 with Apache) take a look at these, and edit your /etc/php/7.0/apache2/php.ini or wherever it is on your system, and changing these values to your liking.