I am not going to get into PC vs Mac for usability. That is a religious discussion. My focus is on PC vs Mac from an author or visitor perspective.
In the browser article we noted in my largest site 66% of the visitors were using Internet Explorer. By definition this is a PC running some flavour of Windows.
Windows is about 88% of my visitors with 7% Mac and 2% Linux and various others like phones. One aspect of a website that is directly effected by operating system of the visitor is video. A video done with Windows Media Player is only viewable by 88% of the visitors (Windows). Flash video puts you closer to 100%.
If you look at sites like CNN.com, all of their video moved from Windows Media Player to Flash video a few months ago. YouTube.com is also Flash video. This is not saying to write a website in Flash. HTML vs Flash is another discussion. All I am saying here is how video is delivered.
Audio on the other hand has standardized to MP3 format. All of the media players (Windows Media Player, Apple Quicktime and Flash media) can play MP3. The only slight wrinkle is Flash can not play all variations of MP3. If you create the audio to play on Flash, it will play on any of the others.
H.264 is the video standard that will change video to the same as audio. During 2009 all of the media services will expand to support H.264.
For now do video in Flash video and it can be viewed on all platforms.
One interesting trend in the PC world is the “netbook.” A netbook is a subcompact PC notebook usually running Windows XP or Linux. Asus started the trend with the Asus EEE. I purchased an EEE then about 6 months later bought an Acer Aspire One. While a real notebook its limited screen (1024×600 8.9″ display) and slower processor is the trade off for a small unit weighing in at 2.2 lbs. For web based authoring where the only real tool needed is a good browser, it is ideal.
Authoring on a personal computer be it PC vs Mac differs in the tools available. If on the other hand you are authoring on this host using an authoring system like WordPress, PC vs Mac makes little difference. The only time the local computer would be used is to compose media such as audio or video or edit an image. Both systems offer excellent tools.