He doesn't jump anymore at all.  I have noticed that his jumping has
tapered off over the last 2 years or so.  Even back in Thailand I would
sometimes see him miss a jump and then he would not try that same jump
again for months and months.
I think he might be more prone to missing jumps because he doesn't have
a tail and so he can be a bit klutzy.
Now he doesn't even bother trying anymore.  He can't get up on the
bathroom counter even though he wants to so badly.  He just paces around
and stands up on his back legs to see the top, but if he can't see it,
he won't jump.  He only even gets up on our pretty high bed because
there is a wide ledge all the way around it at the half way point.  And
he paces around for a while before working up his nerve.
It's definitely not physical though.  He can run and leap and he scraps
with Dennis like a kitten.  I honestly think he has a mental block
against jumping.  The other day I put him up on the kitchen counter and
from there he made his way onto the wine rack (no jumping required) and
from there he jumped onto our Chinese cupboard!  This is the same
distance as jumping from the floor to the bathroom counter would be.
But since he's rarely even been on the wine rack, he probably has never
missed this jump before and therefore wasn't too scared to try it.
What a weird little bugger he is.  But it makes me sad to see him turn
into a bottom dweller :-(