Linux - within a whisker of being able to hold its own as a serious nonproprietary desktop solution?

Yes, according to this 2005/2006 Investigation into the viability of Linux as a Business Desktop Operating System by Stephen Fellowes for the UK Society of Information Technology Management. This ~50 page report [650 kB PDF]  compares 5 different linux-based desktop operating systems, against a range of criteria (installation, first boot, devices and peripherals, applications and file types, systems administration, networking), and includes a focus on their use on laptops computers. It finishes with some pragmatic recommendations for corporate users, concluding that:

• versions with a clear link to a major development partner like SUSE or Novell have a "greater potential to provide a fully functional installation", and
• the support of hardware vendors is crucial to the successful deployment of linux-based operating systems on laptop computers.