I will get some lithium grease and see if I can at least prevent the hinges on frequently used 100-series PBs from stiffening too much. That might help, though actually the ones I have seem reasonably OK, except for the 180c. The 170 is most used of them at present, and it feels reasonably good, but any preventative maintenance is better than none!
I've already broken hinges on my 190 and the less well cared for PDQ, and the 1400c is left permanently open - as is my 190cs - to avoid worsening hinges that are clearly going to fail soon if used, but I don't have much space to put open laptops to store them, so options are limited.
I never did like the 500-series, so those don't get used at all, but I do like the 3400 (I got one after reading about yours) though the screen is slightly floppy when open, so that needs looking at when I get to opening it up to snip the PRAM battery. The 2400 hinges seem fine though.
The Wallstreet and Lombards seem to have pretty solid hinges, as do all the newer models - even the TiBook's hinges are good, though the TiBook itself is basically deceased now.
All in all, maybe I've not done too badly for hinge issues, but maybe I should switch to desktop systems.... except for the plastics issues they all seem to have too!