My first Thinkpad was a well used, well abused Thinkpad 600E. Pentium 2 and 128MB of RAM, with a 20GB hard drive. I used the computer until the trackpoint finally died, then kept using it.. still own it, still works fine to this day.. and I still use it.
Got it in 2006, kept it for the longest time. Like I said, still have her and use her today.
But I didn't truly fall in love with Thinkpads until I used something else. I had an Acer netbook that I used throughout 2009, gave me a lot of troubles.. but not TOO many.
What motivated me to be the Thinkpad fanatic I am, was using an HP G60. That computer was the worst computer I've ever used. Bar none. It overheated, even caught fire once. And it wasn't durable at all.. the case had flexed in the 6 months I owned it, and it went through a fan.
When it finally kicked the bucket, my grandmother purchased me a used IBM Thinkpad R40 from ebay, $50. I missed the superior method of input, and most importantly, the superior build quality a Thinkpad provided. That system lasted for a little over a year before falling fate to the famous GPU issue.. I bet you thought those were only T40s, huh?

Yeah the previous owner pretty much destroyed that old laptop, the case had a few cracks in it when I got it.. the flex was to be expected. Tried reflowing it, failed.. if anyone has a screen and a PM motherboard for one of those that they wanna sell for about $10, PM me.

But for my birthday, my grandmother surprised me even more. She ordered me a refurbished Thinkpad T61 with Intel graphics, and I own it now. The superior build quality, performance, and reliability is back in my hands, and after being abused and left on every day all day, she's working fine with OS X right now. Best computer I've ever owned.
You truly never realize how good these laptops are until you're found using something else. And sure, if you have a Thinkpad, you might buy another brand once.. but I'll bet money you won't buy another brand twice.