I just read that Washoe, the chimp who learned how to sign and taught several other chimps to sign, has died. You may recall that I went to see Washoe back in the summer of '06, when I was on my cross-country trip, and blogged about it.
I think we owe a lot to Washoe and her species in all sorts of ways that we're unlikely to repay adequately.
Where I lived in the Peace Corps, one never said "adios" unless it was pretty much the last time you expected to see someone. So, saying "adios" for me still has that finality to it, even though I'm a total athiest.