Ubuntu has taken quite a bit of flack from the get go for its, uhm... unique... default colour scheme; mostly because the overarching colour of the theme is brown. Now, I myself am quite partial to it. It's warm, welcoming, and a departure from the same old blue- and silver-based themes with which most other operating systems seem to roll off the assembly line. This default theme has been tweaked throughout Ubuntu's various releases, but the main colour palette still remains based around the colour brown.
A sagacious relative of mine bombasted his corpulent cuerpo into my bedroom on a recent visit, and spied my Ubuntu desktop (sporting a modified, but still very much brown, theme). The first words echoing from out of his abysmal estuary described my desktop as "looking like shit." Not in a metaphorical sense, mind you, but in a very literal, faecal one. I shrugged it off and distracted him by tossing an animal cracker down the hall. Nevertheless, this got me thinking. Why would the first thing someone thinks of, when seeing the colour brown, be shit? There's nothing inherently shitty about the colour brown - though, I concede, there's something inherently brown about shit.
When I think of the colour brown, the first thing that pops into my head is chocolate. Something which is a treat: A delicious luxury to be sampled only by the most deserving. Wouldn't this be a very clever - or at least marketable - way to describe a great operating system? Think of a high quality, free operating system as being analogous to a neverending river of chocolate. The former being as much a pleasure to use as the latter is to eat. Except that Ubuntu won't cause you to get fat (in theory). Nor cause you to become diabetic and lead you to a lifetime of health problems and an early death. Okay, come to think of it, maybe chocolate isn't such a marketable analogy, but hey, at least it's not shit.
Another thing that comes to mind when I think of the colour brown is coffee. A delicious beverage with a history as rich as its flavour, and with as many varieties as it has fans; one for every palate. A universally beloved infusion which is welcoming enough to be accessible to the casual drinker, yet still full and complex enough to please the connoisseur. A drink equally at home and appropriate in a professional atmosphere as in a casual one, a pot of which not being out of place in either a cosy room with a few close friends, or the boardroom of a Fortune 500 company.
Wouldn't that last paragraph, awkward though it may be, describe Linux with equal comeliness? Of course it would, because it does.
What it comes down to is that those who attack Ubuntu for adopting a brown default theme for their Linux distribution are really just highlighting their own short-sightedness. Clearly, they feel the need to beset those who dare deviate from the norm of cold, sparse themes which are about as homely as an operating theater.
Your choice of themes, much like your choice of sexual partner, is an individual thing and entirely your own business, but it seems irrational to attack Ubuntu for using a brown default theme, given its warmth, neutrality and individuality.
Mark Shuttleworth has written a great defense of the choice of brown for the default Ubuntu theme, clearly explaining the motivation.
As requested, here's a link to the GTK Dust theme.