Interesting question.
My Mac laptops are superior in their physical design and build quality. This has made them rugged, and they have coped with travel much better than my HP does (I travel frequently, and with both machines, but now with the MacBook Pro, I will only have to take the one machine because it runs Windows too - YAY!). Try integrated camera and infra-red remote control on for size, keyboard backlight, magnetic power connection (which works much better than I thought it would) and the list goes on...
The OS (to me) seems more stable and advanced, so things just seem to work better and with less drama - making my life easier. But I guess this is subjective and depends on what you do with your machine. I would say (from my technical perspecive and my large system background) that the Unix base of Mac OS is what puts it ahead, and creates the stability. But being a Chief Information Officer, I am a geek at heart...
Macs are superior at graphics processing, film and audio editing, mainly because of the OS, embedded technologies such as Quartz and Core Audio, and the great software Apple offer - iLife for the consumer end, and the Pro apps for the high end. However you said that this wasn't a priority for you as you just run Office, so I guess this doesn't apply to you.
I have to say that iWork is a real advantage, especially the presentation program Keynote. It kicks ass, has styles and effects no one else has seen before, so if you give presentations, Keynote gives you the edge because your audience has seen the capabilities of powerpoint before. Let me tell you this, the first time I wheeled my Mac into the Boardroom, there was scoffing, but after I finished my presentation - they clapped. Not having pepople drift off in your presentation means you get your message across.
A related feature that is nifty is Salling Clicker, remote control software that works over bluetooth to control applications on the Mac, including the presentation software. For Powerpoint for the Mac you get the slide notes on the PDA screen, with Keynote it is just a simple navigation remote - but Keynote has the best presenter display I have seen (current slide, next slide and your speaker notes on the laptop screen, presentation on the projector). This Clicker software allows you to roam the room and get close to your audience (bluetooth works up to 10m away), and control your presentation like a pro - very impressive to your audience. Most don't see my PDA and think I have timed it to automatic slide transitions
I don't know of any similar software for the PC.
AirTunes capability of Apple wireless networking. With Airport Express devices connected to your stereo you can play iTunes music wirelessly. My music thus follows me to any of the 3 stereo systems in my house... you can do this on Windows too with iTunes for PC and Airport Expresses.
I said intersting question because discusing the individual parts does not create a compelling answer really, it is really a synergy thing... my best advice is to try using one for yourself and see how you like it. Some people hate Macs for the same reasons I prefer not to use Windows - it doesn't think like they do, ie they don't feel that using it is intuitive. I don't think this is something that someone can convince you of just by discussion alone, I think you really have to use one and decide for yourself.
In the beginning I thought all the media features were not necessary and I would never use them, they are so easy to use that now I can't do without them. Case in point - a friend from Switzerland - Stephanie is staying with me and leaves soon. When she goes I will hand her a DVD she can play in a normal DVD player with a slideshow of all the photos we took while she was here set to music. This will take no effort to produce (except for choosing music and sequencing the photos), and my prototype I showed her has absolutely knocked her socks off - now a happy Steph is priceless
You can probably do all these things on a PC. But at the end of the day it is much much easier on a Mac because they are designed to do these things all the time, and you get a hell of a lot of software from Apple as standard.
I do have to say that in its early days I liked XP, mainly because it was such a huge leap forward from Win 2K. But I think XP is a pretty facade over some awful architecture - namely Windows NT with some tweaks. I am very interested in Vista, but I think it has been too de-featured over time because MS can't seem to keep to a development schedule.
So I know this is a long winded answer, and probably a little too detailed, but I guess it is an interesting question, and my honest response is that my reasons for preferring the Mac (and I have only had one at home for 1 year now, prior to that had mostly PCs) are complex and deep.
I am sure that this post will generate a lot of discussion...