Don't pitch it as perfect (it isn't), suggest key features:
Exposé, no ALT+1234 to get accents, ease of application installation & removal, Column view finder, unix-ness, apache & other "sharing" stuff from the get go, ilife (only if he'll use it), this is a really long list
you don't have to mention everything.
As for speed complaints, my argument tends to be "A pc is has really fast hardware, i'm not denyinng that, and it saves the computer a lot of time, but on a mac its all about saving you time (and frustration)", (this really applies to laptops more so than desktops) then give them an example, or several based on all the features you are focusing on.
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edit:
I didn't mention security / viruses. A little story: I had my mac for about 2 months, and it was great. Then I went home (i'm a college student) for break, and wanted to check my email so I fired up my mother's computer (win xp) and *BAM* 5 minutes later a worm had infected the computer. I was on dial up, so I couldn't run virus update, or google a solution, so I had to call someone up and ask them to google it for me. So my 5 minute email check turned into an hour of chaos + 5 minutes to find out I didn't get any email.