Yeah i have had all the D600's series from Dell, let me start with the specs of each laptop so you have an idea on how im comparing each laptop.

D600

1.4 PM 512MB 40 HDD 32mb ATI Screen SXGA+ DVDRW+/-

D610

1.8 PM 512MB 60HDD 64mb ATI Screen SXGA+ DVDRW+/-

D620

2.16 Dual Core 1GIG 80HDD 256 NVIDIA Screen WXGA+ DVDRW+/-

Let me say that the D600 vs the D610 you wont notice that much of a difference the only good thing is that the D610 has more usb ports and the touchpad looks nice besides that they are the same computer, you can beat the crap out of these computers and they will still work, nice model for anyone that is in the construction or some one that just doesnt take care of computers, the battery on both laptops are almost the same giving me about an hour or 1 1/2 depending if im using the optical drive, the screen on both of these laptops are great for watching DVD's or just using them for office work, I will give Dell a 10 for  creating these laptops (if your asking yes i also had a couple of the C series)

NOW LETS TALK ABOUT THE D620

I was thinking about buying this laptop because of the buzz of the dual core, it turns out that I drop my laptop on some wet concrete and Dell sent me a replacement (on the D600 since I had complete care warranty on the system), I was so happy when my wife told me that the computer came in (was out of town because of a buisness trip), came home and gave my wife back her D610, open the box and it looked better in person that it looked in pics, I installed all my programs and since the specs were great I installed CAD, everything was working fine, the next week I had to travel and I took the laptop on the plane I started to watch a DVD and the screen looks HORRIBLE!!! tried another movie that is widescreen same thing, called Dell tech support and they gave me the run around replaced the screen same thing, THE LAPTOP DOES WHAT IT NEEDS WORK WORK & MORE WORK (it runs great using CAD or CHIEF) YOU ARE NOT GOING TO BE A HAPPY CAMPER IF YOU ARE LOOKING FOR THIS COMPUTER TO WATCH MOVIES OR PLAY GAMES, I will give this computer a 8.

Dell you  cant make every computer a 10 you made a mistake with this one (D620) thank god I didnt have to pay for it, hope you fix the problems with the other 600's series that are to come.

BOTTOM LINE

IF YOU HAVE A D600 OR D610 & you are planing to upgrade your computers buy one and check it out, before you make a mistake, personally I'm going to keep on running my buisness with D600 & D610 until Dell changes the D620 with another computer or fixes the issue with the screen.