I went on a little adventure the other week of setting up my own NAS server, and checked out Owncloud and competitors. Even ignoring issues like feature parity and third-party app integration, I think the setup costs of something like this are still way too high for consumers. While VPS providers may make this process easier (even deploying complete Dropbox clones with no tech knowledge required), they'd still be doing it at a significant disadvantage to Dropbox's scale and expertise. It was clear to me very quickly just how much work has gone into giving Dropbox the level of polish it has. Note that this doesn't even address other competitive moats such as brand recognition and distribution partnerships.

Not saying that Dropbox doesn't face business risks -- but I think the open-source alternatives will not be the biggest risk ulttimately in the mainstream market.

I do think they will face margin pressures as long as Google/MSFT/Apple/Amazon believe this to be too important of a market to cede to Dropbox.

though things like Owncloud help make it easier for self hosting, many enterprises will still prefer to opt for something like Dropbox because Operations are hard!

Why does anyone use hosted travis CI despite being able to run it ourselves? Why do people use google apps instead of hosting their own mail servers? Because instead of having your employees do something they're not necessarily good at, you will pay experts to do something they are (supposedly) good at for a fraction of the price.

Yes because Owncloud will never get the kind of adoption that Dropbox has specifically because it isn't consumer oriented.

It's just like Linux. It can own the backend / developer world, but Linux is still no where on the desktop for the average consumer.