Microsoft doesn't want you to use open source software. And the way they get you not to use open source software is through FUD. The latest example can be found here, where MS is "indoctrinating" sales staff in the reasons customers wouldn't be happy with Linux.
Now it's perfectly true that Linux doesn't run Windows programs. If you really want to run MS Word, you'll need Windows; but if you use Open Office, you won't. Fair enough, customers should know this.
Linux doesn't run Windows games* (*Some will run in Wine, but the performance can be poor.) If customers want a games machine, they'll need Windows, fair enough, although I actually think a dedicated games console can be a better option- games take up huge amounts of disc space, require a powerful video card which can add the price of a games console to a PC, and if my experience with Half Life is anything to go by, can rip a HD to shreds with crashes while reading or writing to the HD leaving bad sectors.
Now we come to hardware. My printer, camera, MP3 player, wireless dongle and external hard drive all ran out of the box on Ubuntu Linux. I had to install some firmware for the scanner to work, but I'd've had to install a driver for it to work in Windows- in fact my printer doesn't work in Windows because I haven't installed the driver. Good manufactures support standards and Linux, and their hardware works in Linux. (HP is a shining example.) Verdict: FUD.
Finally, Internet Messaging. No, you can't get Window's Live Messenger on Linux. Yes, you can have IM with a multi-protocol IM client* like, in Ubuntu, Pidgin. (* Supports multiple accounts- MSN, Yahoo!, Google, ICQ etc.) No, Pidgin doesn't support video chat on MSN (and I don't know of any Linux IM client that does.) Linux does have Ekiga, a free video chat client, and Pidgin does support video chat on GMail, but I can see that it's not going to be convenient for a Windows users to get used to a new IM program, or a Linux user to video chat to a Windows user.
This is a big turn-off for prospective Linux users, or indeed, purchasers of Linux computers (netbooks, probably) who ask: where's Windows Messenger?
This is of course intentional: that's the way Microsoft works: get you used to their product so it's just too much effort to change.
Verdict:FUD. There's no reason to be locked in to Windows. There are alternatives to the Microsoft IM network.