I had a 600m for a while (on my last job) and liked it very much. It was the perfect size for travel, without sacrificing anything other laptops would have. I definitely prefer it to the IBM Thinkpad T42 I have to use for work now. The only laptop I've had that I liked better than the Dell Inspiron is the Apple Powerbook.
I have used a Dell c600 for several years now and it has been a real workhorse. I live in upstate NY and have spent over 100 nights one year in hotels. My laptop has weathered subzero to over 100 degree travel temps and lasted. My previous laptop was also a Dell and it still works although it is too slow for my current needs.