Hi. I thought I'd weigh in my own thoughts on this since we migrated from using Dropbox to Owncloud.
What I would highly recommend before migrating is looking at something like the virtual applience on Bitnami first to have a play with and explore Owncloud.
There's lots of good things such as ease of use, it's configurable, it can do audit trailing (what they call "Activities", it can tie in to LDAP (be it Active Directory or Open Directory) normally very easily and nicely, being able to give users limits for their own accounts, so for example, someone can only have 1GB worth of storage, another can have 500GB of storage, obviously depending on your server/hosting back end.
Tags and comments which are relatively new in version 9 are a nice addition and can make searching for data easier, so thumbs up there!
Installation on a server we have in house was pretty quick and easy, though if you are going to host it in house/manually, I'd highly suggest someone with knowledge of Linux Servers, CSS, MYSQL and also someone who is knowledge about port forwarding and any firewall solutions you have in play is involved in the process.
The Owncloud desktop and mobile apps are fine. Given they're free, I'd say they were good, and if you've used Dropbox apps on your mobile or desktop platforms, the Owncloud ones work in a very similar way
We have hit a couple of issues with pages loading a bit slow in version 9, but nothing that's a show stopper by any means (and during peak times we have 40+ people using it internally and externally), and that's probably down to me not doing something correct and hosting it on an non-supported platform (MacOS Server).
If you do share a link externally, also note that in the audit trail/activities just appears to say the file has been downloaded vs. putting someones name against it, unless that person actually logs in to the server as an actual user.
I think the main thing is to have a play with a virtual or test applience and see how well you like it. So far aside from a few bugs which were sorted pretty quickly, it's all been happy days.