1) Linux will behave like Windows.
The misconception that one OS acts just like another makes me crazy. It's like me going from a Toyota Prius to a sixteen wheeler "big rig" and expecting it to handle exactly the same.
The fact of the matter is that the Linux desktop has no singular way of presenting itself. That's the power behind Linux on the desktop. It can be customized for different needs and distributions, while relying on a variety of desktop and software packages to make it work a certain way.
Windows, on the other hand, has a "here it is" approach that works well enough for its intended audience.
2) Windows software looks better than Linux software. So you think that Windows software has the marketplace cornered on what's pretty? Take a look at some of the horrid looking applications running under the shareware/freeware license sometime.
And while you're at it, be prepared to be turned off cold with some very unattractive software. The fact of the matter is that all platforms have software that can look great as well as some that are horribly ugly.
Best to leave the complaint of "software sex appeal" to the individual application itself, rather than blaming the entire platform. Looking for pretty software? Try the KDE desktop. By its very nature, KDE applications tend to be more visually exciting than their GNOME counterparts. As to the functionality of each application, that really comes down to user preference.
3) You have to be a geek to operate Linux.
How many non-geeks do you know that install their own operating systems? One? Zero? There's my point no one except advanced users or "geeks" actually install operating systems without help from someone much more tech proficient.
As for the operation of the operating system, Linux on the desktop has been used for years in schools and retirement communities. Clearly, any perceived user difficulty is overcome quickly when the technical details are left to the professionals.
4) There is no software available for Linux.
Your legacy software titles may not be available for the Linux desktop. This may mean using Firefox rather than Internet Explorer, OpenOffice/LibreOffice rather than Microsoft Office, and so on.
As for the sheer number of software titles available for Linux users, the actual number made available really comes down to the Linux distribution being used. Not counting that there are hundreds of titles outside of common software repositories available, Ubuntu, for instance, has 2,334+ supported titles available. This number doesnt include Canonical Partners for purchase options or even the PPA repository-based applications that can easily be installed as well.
5) Installing software on Linux is difficult.
If you're trying to use Slackware or something else aimed at advanced Linux enthusiasts, I might be inclined to agree that this is more difficult. On the other hand, if you're talking about using Debian-based distributions of Linux, I would point out that installing software is easier than it is on the Windows platform.
Ubuntu, for example, provides a Software Center than makes installation and removal so simple that even first time desktop Linux users find success without any coaching.
6) Linux is terrible for small businesses.
Speaking as someone who has supported small businesses that run Linux desktops, I'd suggest to doubters that a great experience was had by everyone involved. Not spending my own days removing Windows malware, and no longer worrying about those "mystery executables" that appeared on the desktop proved to be a massive time saver.
As for the company's experience running Linux on their desktop machines, the switch was generally painless. Linux point of sale (POS) systems, Scribus, OpenOffice, etc, for the rest of their software needs meant no friction suffered by anyone. Anything that was needed was available once I just took the time to look for it.
The biggest challenge is getting the Linux desktop to feel as familiar as possible. Thankfully, customizing Linux on the desktop is fairly straight forward for an advanced user offering support to those in need.
7) You cannot watch movies on Linux.
Whether or not someone can view a movie on the Linux desktop comes down to how it's being viewed. If you're looking for a way to "legally" view DVDs on your Linux desktop (in the U.S.), the Fluendo DVD Player addresses this nicely. If you're looking for Blu-ray support, it can be done, but not legally.
In my opinion the best way to enjoy video content with Linux is to stick to the TV set and a Linux-powered Roku box. This provides you with both Amazon's Unbox service in addition to movie services from Netflix.
8) Linux has no quality control because everything is freely available.
Let's revisit what I said previously about freeware/shareware software. The quality or lack thereof really comes down to the developers of a specific application. Yet because most Linux desktop software is written with the ability to improve upon it without fear of lawsuit, no one is stopping anyone from taking a great idea and repackaging it with a better focus on quality.
With most Linux software, quality control is lead by the community of individuals using the software.