Since web services started, I've always been wary of them & have preached to my customers the pros and cons of them.  I personally don't like  a company possibly holding me hostage to either their whims or profit.  Because you can be sure that very soon one of these companies will look at the profit potential of saying "if you don't want to lose your data, we can save it for you at the new company at such and such price!"

Reminds me of the political situation America is in with the Oil Countries - they've got us by the balls because we need the oil.