Problems with my T61
The biggest ongoing problem with my T61 was the heat production, I’m not sure how much of it was due to the CPU producing heat and how much was due to the cooling system not removing it fast enough. But any serious computation for even a relatively small amount of time caused it to get close to thermal shutdown. But as I mostly use my laptop for reading email, a SSH client, and coding (for which the big compiles are done on servers) that didn’t force me to replace it. The next problem was the battery life, it’s expected that laptop batteries degrade over time so it wasn’t a surprise that after 3 years my T61 battery only lasted for about 15 minutes. A final problem is the screen which didn’t seem to be as bright as it used to be, it’s annoying but doesn’t compel me to buy a replacement.
But in July my T61 stopped working, it appeared to be either the power supply or something internal related to power, it had been running but was suddenly powered down after being left alone so for some reason power wasn’t getting from the wall to the laptop. I initially thought that it was the power supply at fault and investigated the price of a new PSU and a new battery as well. The Lenovo online store  charges $71.90 for a new PSU and $113 for a regular capacity battery or $156 for an extended capacity battery (50% more power). So based on the assumption that the PSU was faulty that meant a cost of $185 or $228 (maybe more if postage is included) to get the old Thinkpad going again. I could probably get the parts cheaper from somewhere else, but I’m hesitant to buy batteries from sources that aren’t reliable in case I get one that’s been used.
Buying at Auction
I ended up buying a refurbished Thinkpad T420 (product ID 4236-J73) from Grays Online . It was refurbished and cost me $306.35 including delivery. $306.35 for a new laptop including PSU was a much better deal than buying a new PSU and battery for $185 or more. It turned out that the PSU wasn’t broken (a different PSU also didn’t work with it) but then my Thinkpad T61 just started working again, presumably it has some intermittent fault related to power and needed to be replaced anyway (I use my laptop for work and can’t have it fail randomly).
Comparing T61 and T420
I upgraded my new Thinkpad to 8G of RAM because RAM is really cheap. I bought it with 4G of RAM which didn’t seem to be quite enough as the hard drive is slow for paging (my desktop with 3G of RAM and a SSD performed well for similar tasks). Now it’s running really well, my new Thinkpad is a lot cooler than the old one (not being broken is a good thing).
My T420 has a screen resolution of 1600*900 which was a little disappointing initially when going from 1680*1050 (18% fewer pixels and 2% fewer than the T41p I used previously). But having a smaller screen means that the Thinkpad is a lot smaller and lighter. My T61 didn’t fit in most backpacks and laptop bags and was unreasonably heavy, it’s the type of laptop that looks good on a spec sheet but doesn’t seem so good when you carry it around for a few hours. Not only is the T420 a lot smaller and lighter than the T61 but the power supply that shipped with it is a lot smaller and lighter too. I might have spent $72 a few years ago to buy a lighter PSU if I knew that was an option.
Cost of Ownership
Thinkpads are getting so cheap at auction that I’m tempted to buy myself an X series as well. When a $300 item can last several years (my T41p was from some time before 2006, my T61 was from 2010, and my latest is from 2013) that brings the cost of ownership down to something like $0.25 per day. If I bought myself a Thinkpad X series (ultra light) as well at auction then I would be looking at maybe $0.50 per day for my laptop use which would give me the option of taking a light laptop to a conference and a bigger laptop for spending a day at a client site.