Francois, I haven't done any UI for over 5 years, but if you want familiarity and acceptability, model your interfaces on something like Outlook. Most if not all of your customers will use it, at home if not at work, so it'll seem immediately comfortable and familiar. Then you can shrug and observe that MS spends millions of dollars to come up with functional UI standards for Windows apps, so of course your firm offers a professional compliant version rather than a colorful cartoon version. ;-)
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
