Simon Phipps - Freedom To Leave:

"If "interoperability" meant "import only", I'd never feel safe trying new things so market growth and innovation would be inhibited. People who implement open standards like this are smart, because although they allow customers to leave for greener pastures they also allow them to return - I am still using Bloglines despite the appeal of BlogBridge - and the confidence I feel over "owning" my data makes me a much more interesting customer.

That feeling is caused by more than interoperability - it takes full substitutability for me to have the confidence to stay as well as the freedom to leave. "