I have a cheap hosting account into which I've extracted the ownCloud tarball[0]. For security updates, I've subscribed to the announcements ownCloud mailing list [1] so I get an email each time there's a new version (either bugfix or major). The mailing list is very low traffic (only messages about new versions). I either follow the instructions on the site [2] for major upgrades or otherwise use the built in updater [3][4] for the minor bugfix releases.
If your pi is just running ownCloud and it's got access to a relatively fast connection, there shouldn't be any problem with doing that.
I'm thinking of getting a VPS to run my own server as the limitations of a hosted account are pretty important when it comes to running your own stuff (as opposed to 'just' hosting a blog or whatever).
I have done this. It's ok, but you have to tinker a bit to get big (GB+- is that even big anymore?) files to upload with the web interface. It might be worth your while to get something a bit more powerful (sheevaplug, etc.)