I'm in a similar position. I have a T60 right now, and I have been considering upgrading to a T430, but I really don't have a huge need to. My laptop runs fast enough for the stuff I use it for, and it's still in good condition (but I'd still love to get a new, faster computer).
I've been using the laptop practically every day for the past 4 years, carrying it to campus, etc, and it's been holding up quite well. The only downside is that they don't offer very good graphics cards for it, so it wouldn't make a good gaming computer. It does have a really nice keyboard thought, and makes a great development PC.
The nice thing is that complete ThinkPads of the T60/T61 vintage with a decent battery, AC adapater, and HD still command a decent premium in the used market. Hell I got $175 for a T23 about a year ago.
The market is flush with system off corporate lease, but they rarely include the above items.
I've been using the laptop practically every day for the past 4 years, carrying it to campus, etc, and it's been holding up quite well. The only downside is that they don't offer very good graphics cards for it, so it wouldn't make a good gaming computer. It does have a really nice keyboard thought, and makes a great development PC.