Certainly. That's what I'm here for.
I had an 8887, I don't know if you knew that.
Anyways, here are some reasons I chose the powerbook over the 5670, or the 8887 (I am a seasoned veteran of Windows, and various UNIX flavors, along with OSX)
1) UNIX. Mac OS X is UNIX-based. I cannot state how great this is. Often times, there are software which are available and open-source, which are worth your time. It's not hard to port applications from UNIX to OSX. It usually requires you to type ./configure, make, and then sudo make install. Not hard.
2) Gaming is decent. If you feel like sitting back and playing a game, the Mac has a fair assortment of games. PCs have more games, and play some games better, but the powerbook with the GeForce 440 Go outperformed the Sager with the M9 128MB in Quake3. Take that as you want. The mac has a large quantity of available games. Check out www.macgamer.com
3) The screen is gorgeous. Though the viewing angles aren't as good as the 5670, there's a certain clarity you get with the mac, which is unparallelled by anything. Images just look right. Apple's colorsync also helps with all this.
4) Asthetics. The aesthetics of the 5670 aren't quite on par with the asthetics of the powerbook. You can use the powerbook on your lap. The 5670 requires a hard service for the fans to work properly.
5) iTunes. If you do ANY music on your computer. Not just editing, but listening. iTunes is a MUST. If you set up and use iTunes as your music player, you will most certainly NOT be disappointed. It handles every language I've thrown at it (I speak over 15 languages, and listen to music in about 7 or 8 languages. Thai, Korean, Japanese, English, Hindi, Urdu, and Punjabi.) It is great for ripping, mixing, burning, listening, and using. It's hard to explain its greatness.
6) Portability. The sager isn't a laptop. It's a condensed, portable desktop. While some people find this a plus, it's always very nice to be able to use the computer on your lap, or in the car, without some sort of special tray.
7) Mac-Only software. Final Cut Pro: Best video editing app. Logic: Best Music App (some think Reason is, others think Reaktor is... they're all around on the Mac. Hey, so is Protools, but most audiofiles aren't into protools.) DVD Studio Pro: Awesome. Shake, again awesome. Then the iPhoto, iMovie, iTunes, iSync, and all the iApps are pure brilliance. Not to mention the things you can do with UNIX that windows users cannot.
8) DVD Burner. Though the sager has this as an option, there is not a large quantity of good dvd-burning software for windows. Macs treat DVD burning really well. Check out Toast, DVD Studio Pro, and hey, you can burn DVDs from the Finder with no problem.
9) Tomorrow. A new mac OS comes out every year. Mac OS X 10.3, Panther, will be out in August, most likely. It will feature things we can only dream of. For example, rumors indicate it will have a BeOS-like filesystem, which is superior to Windows's filesystem in Longhorn.
10) Durability. I don't know how durable the 5660 is, but I dropped this powerbook from about 5 feet in the air onto a brick fireplace by accident. Not a scratch. Not a dent. Nothing. I was hideously worried I would have broken something, but the laptop is still fine.
I hope this list has helped you. The sagers are awesome too (as long as yours isn't defective, as mine unfortunately was, so I'm a tidbit biased.) But the mac has the advantage for the creative person. I think David Coursey said "If you have even one creative bone in your body, the mac will appeal to you." I full-heartedly agree. PC's tend to be for mainstream things, but I don't think people are mainstream... Everyone's unique, and macs are unique.
Good luck in making the right choice. Both apple and sager have return policies... so you'll be OK.