JSON has actually eclipsed S-expressions for me as the most obvious way to structure data. JSON effectively gives into the lure of alists and commits to them in a pretty obvious way.Although he thinks more favorably about XML than I do. XML could not go away soon enough for me.
Also, in both JSON and S expressions, the concrete syntax is so trivial (and orthogonal to the model) that it doesn't really get in my way.
I can't say the same for XML.
Surprisingly I do prefer JSON as an exchange format that Lisp (sexprs). For the reason Don gives above... it is very easy to see the alists and the arrays (true lists) in JSON than it is in Lisp.
So while I would dearly prefer to program in Lisp (Scheme) than any other language, I would want to exchange data via JSON.
Not a problem... in Common Lisp, Gambit Scheme, and several others, the neat thing to do is create the read-table syntax for JSON.