I read much concern about how our privacy is threatened by all sorts of companies, such as Google (who knows everything about your secret desires) and Facebook (who knows all of your friends’ birthdays).
My biggest concern relating to all these services is externalisation, which comes at the price of loss of control over the service or your data, or both. What happens if tomorrow Facebook decides to charge you 5 euro a month for their service? Chances are there would be an uproar at first, then most users would consider that it’s too small a price to pay to worry about it. Yet they’d never have joined in the first place, had the service not been free in the first place.
Something similar happened to me recently: I used Haloscan to manage comments on this blog. Haloscan was free, easy to integrate and convenient: it did everything magically, filtered spam out, provided RSS feeds for comments and so on. And then inevitably one day they ran out of resources and slashed their free offers. I no longer have comments on my blog.
External services are like the dark side of the force: they are easier, faster, but ultimately not as powerful as doing things the right way, which is hosting everything for yourself. Only then do you know your service will survive the stand of time. Well, as long as you pay for your ISP bill I guess.
Eben Moglen expressed somewhat similar thoughts (although mostly from the point of view of privacy, which is another facet to the control of your own data) in a very interesting, recent interview.