> Are they profitable?
Profitability isn't the end-all metric for a company. Amazon famously circles around the profitable/not-profitable line frequently and few people have doubts about Amazon's viability as a company.
Dropbox reported ~20% growth in revenue YoY and seems to have dumped most of that into R&D (you can see their R&D costs have grown by nearly as much as their revenue has). Other operating expenses remain mostly the same.
> There is no better evidence that Dropbox is just a feature than for the same price that Dropbox charges for 1Tb of storage, you can get the full Microsoft Office Suite for up to six users and a total of 6TB of storage.
Ok, but a growing subset of people clearly choose Dropbox. There are huge advantages to being a first mover that are sometimes insurmountable, even for gigantic companies. The zune was in many ways "superior" to the iPod, but we all know how that story ended.