You're not missing out on anything, there are no significant advantages (specially not over a t61) I sold my powerbook on ebay, and I'm still happy with my t42 running gutsy as well.
I've noticed both Apple and IBM/Lenovo dropping in quality over the past 10 years or so. I have a Thinkpad 600X from 1998 or so - it's made mostly of carbon fiber, with a rubber coating. My Z61m is made mostly of cheap plastic, though it does have a metal frame and titanium lid. Apple uses either polycarbonate or aluminum, but seems to have a high rate of logic board failures. I'm not a huge fan of metal on the surfaces of a laptop that come in to contact with my body during use either - it transmits heat.