Just to clarify my position, I never meant to imply that real work couldn't be done on Windows boxes -- just that it would be difficult to be productive on cheap Windows boxes. Cheap computers, regardless of the OS they run, server nobody well.
Perhaps, but my personal experience says otherwise.
'Cheap' is a relative term (and I think you need to be more clear by what you mean by 'productive').
Although, if we are talking about low-budget computers, one can actually be very productive on them.
For example, I bought an Dell Inspiron 1300 in the summer of 2006 (almost 4 years ago). It came with 512Mb RAM, a Celeron M cpu at 1.6 GhZ, 80GB hdd, and a very old integrated Intel GMA card.
It wasn't powerful by any stretch of the word (it was low-budget after all), but it was what I could afford at the time.
I was able to do 3d Art on it with relative ease (comparable to what I was doing on my desktop computer with dedicated graphics), not to mention I also used Photoshop for image processing (native resolution sized images), e-mails, Internet, youtube videos, and even some gaming (actual 3d games that were a few years older though, but still, my demands were not high).
I was very productive on that low budget machine (3d art is extremely cpu/resource intensive btw and I was working with scenes containing meshes that had over 1 million poligons at the time), so I would have to say it mostly depends on the hardware you have, and how you can make the most of it (the problem is that a lot of people are not well aware of what they are getting and therefore do not know how to use it).
I gave that laptop to my mother over a year ago (who isn't a computer buff by any stretch of the word, and only uses it for some writing), but it also received an upgraded HDD (160 GB), 2GB of RAM, and I oc-ed the cpu to 2.1 Ghz - which is holding for over 2 years now without overheating when stressed.
It is running Windows 7 without any issues whatsoever - it even beats slightly my desktop AMD XP 2600+ when it comes to that OS and responsiveness, and both have 2 GB of RAM - it's likely due to the HDD though).
Perhaps my case is an exception, but speaking from experience (and that of other computer savvy people), it usually (but not always) comes down to the users and what they do (or can do) with their computers.
I think we went too much off topic though.

My apologies for contributing to it.