Willow bark's an odd one at times.
It makes really good cordage, if used wet. It's among the earliest surviving examples in Europe, but only when found in wet situations.
If you really have to chew the bark to get the pain relief look for goat willow, it's sweeter tasting and every bit as effective.
Best not to do it on an empty stomach though.
The OP asked about it's use as tinder....the little downy catkins work well, and the twigs and barks as extenders, but it's as charcoal that it really comes into it's own.
The charcoal not only burns well, but if ground down to fine and taken as a tea (pretty gross) it helps stop the trots and eases windy indigestion.
Old English books, herbals and almanacs call it willowfine. It's an anti inflammatory and eases arthritic pain (and toothache, incidentally; not an excuse not to see the dentist but it'll tide you over when you're out and something flares up) it doesn't work as quickly as the commercial products as a pain killer, but the effects seem to come on slow and linger for longer. You don't need to take another dose in the middle of the night kind of thing.
Very good for backache ( probably why w00dsmoke said how bitter it was ? ) and long lasting aching pains from joints and tendons.
Good for mentruation cramps and aches; very soothing.
There are some valid contra-indications though.....not good at all if you have ulcers, don't use if a rash develops (usually neck and chest) and don't mix it with prescription drugs since it interferes with some. Asthmatics are also best to be very wary of it.
It's very good for 'flu symptoms but nowadays, since it's an 'aspirin', definitely not advised for children.
Well worth becoming familiar with the willows
exceptionally useful trees
cheers,
Toddy