Also addressing similar needs, maybe worse than iFolder but surely better than the "other systems" cited in this article : all SCM, in particular distributed one like Git or Mercurial do allow "clients continue to work while disconnected from the server or the network as a whole" and doesn't "requires kernel-level support on the client machine" either.
Indeed DSCM (+ properly configured cron/icron/at jobs) do have different strengths (ie. change history, N-way manual merges, ...) and weakness (ie. spreading .git/-like directories all over the place, lack of high level frontend to configure them for such an use, ...), but at least an Unison vs. iFolder feature comparison would be more useful (look, they even are both candidate for the "unexpected programming language choice" ;) than an apple-to-orange comparison with Coda or NFS.
Unrelated question : the article's description make it look like iFolder is re-scanning the whole directory tree at regular intervals.
Can't iFolder just scan once at server connection, then passively monitor & propagate immediately via inotify/gamin/fam ? Else, what the cost in terms of resources (power consumption), and isn't it too much racy ? (risk to loose changes when shutting down laptopA and switching to laptopB, if changes are only looked for and replicated every few minutes) ?