First, Thanks to this community. I was googling my T40 USB issue (randomly reverts to 1.1), and ran across discussions on this forum about it. I've now got this forum in my favorites. Great info here!
One person had mentioned that twisting the laptop could aggravate the condition, so I tried it, and my random problem turned out to be not so random. I could make it do it by twisting it every time.
So, I took the palm rest and keyboard off and started poking around, and noticed that if I press from the bottom right under the southbridge I could get it to do it (the southbridge has the USB controller in it).
I pulled the datasheet on the southbridge and noticed that the USB pins were in the lower left corner.
Now for the fix (I don't necessarily recommend doing it, but here it is):
I reflowed the solder on the southbridge using a heatgun (one designed for soldering, but not necessarily designed for BGAs). I took some tips from youtube from the guys who did the same for video chip problems. I monitored the temp with my IR gun, covered the nearby connectors, and focused mostly on the lower left corner where the USB pins reside). One nice thing is that there are some epoxy balls holding the chip, which minimizes the possibility of it getting miss-aligned.
So far, works great, even with moderate twisting of the board. It was very repeatable and frequent, so even though it's been only a day, I'm fairly confident that it's fixed!