Mac all the way. Me, longtime user.
But my business partner, a longtime PC user switched last year. That was quite telling to me.
The initial reasons: Better color calibration out of the box, easier for us to deal with print houses on any print work, almost no viruses, no spyware. I use an iMac G5 20, he an iMac Intel Core2 duo 20. Both are great machines.
But once my friend got his machine, we discovered many other benefits: The bundled software such as iPhoto and iWeb are way more useful than you might think at first.
We used iPhoto alongside Photoshop to orgqanize and cull photos -- much easier than Photoshop alone (we are now migrating to Aperture alongside Photoshop. Aperture is a great program as well; really manages project and photos well and organizes things.)
iWeb builds great Web sites (poo poo it if you want, but the bottom line is that we are now maintaining and growing our site -- and our business, instead of watching mold grow) and iCal -- tied to DotMac -- has allowed us to integrate our wedding photography assignments, meetings, portrait shoots and sales calls into one convenient calendar we can access in iCal at home, or from anywhere (Mac or PC) in the world. It even sends appointment reminders.
Overall, very solid and stable. Bottom line: It lets us do our work with minimal intereference from the OS.
Good luck; you should love the new laptop. Just remember, Mac or PC: Just a tool; the photo begins with your vision.
Pete