I recently purchased a Dell Inspiron 8600 and I am very pleased. I use this machine for gaming and as my primary machine at work. It is very quick, has a 1920x1200 WUXGA screen, built in Wi-Fi, 60GB 7200RPM drive. It gives my desktop at home (2000XP+, 1GB RAM, 8MB cache 80GB HDD, Radeon 9600Pro 128MB) a run for its money. The video is on par if not a bit faster than my desktop (I have a 128MB ATI 9600 Pro Turbo in the laptop) and the applications run at about the same speed. Battery is good for about 4 hours with moderate power saving enabled while using office apps (I never game on the batteries other than solitaire so I don't know about gaming battery life).
All in all, I would recommend this system to anyone looking for a desktop replacement for gaming or other apps. However, if you want raw CPU power, the Dell Inspiron 5150 can handle a 3+Ghz Hyper Threading P4. It doesn't have as good of graphics options though. Another reason I would recommend Dell is the warranty and support. I have only had one problem with Dell support (it was a misunderstanding regarding a replacement WiFi antena which was resolved within 1 week) and I have owned three Dell laptops (I5000, I8200, I8600). I purchased the 4 year warranty with complete care so even if I spill coffee into the machine (not that I haven't done THAT before

) it is covered.
Just my 2 cents. Your mileage may vary.