I just now noticed (June of '10) that Gido reprinted the posting I made on our yahoo group "perfumemaking" (which is indeed wonderful). I'm grateful that my words are of some use to you here as well.
I noticed a couple of typos and remarks I should amend for the record.
I misspelled the proper chemical name for Hedione, so beloved since its use in Eau Sauvage brought its magic to the attention of all perfumers around the globe.
It's spelled methyl dihydrojasmonate. I stuck a stray "n" in there.
I neglected to mention two other important classes of perfumery molecules; the ethers, which are at least as stable as ketones –and lactones, which are a special subgroup of esters, actually. The difference is that lactones are made from molecules which are, shall we say, hermaphrodites? They form an ester with themselves, having one part of their molecule be an alcohol and another part of themselves an acid. They, well, they sorta "copulate" with themselves
and form a circular structure of some type. Some very important musks are lactones, such as pentadecalactone. Some provide useful coconutty and peachy notes. Another oddball is ethylene brassylate, a very useful musk consisting of a double-ended long chain acid plugged in at both ends to a double ended alcohol.. technically an ester or lactone however you choose to view it. Again it's a sort of circle well-you-know-what.
A lot of the chems used in fragrancing aren't simply one class or another. Many, many valuable molecules consist of any combination of the listed classes, depending upon where you look on the molecule.
I just read back and see that I did mention that fact, but it's still worth repeating.
One more thing: Sulfur-containing molecules are more useful in perfumery than my posting suggests. Their use is increasing as perfumers learn to work with these mostly hyper-potent chems. They often provide exotic fruity notes, like mango, passionfruit, etc, which have come more into vogue, thanks both to consumers' taste and also their slow introduction to perfumers. The same goes for some sulfurous nutty / coffee / chocolate notes which lie at the basis of the foody/gourmand trend.
I will be posting a very interesting article, I think, about "watery/fresh air/ozonic" type notes and a bit of history about why we perceive them as we do.
I'll have it up on http://michaelstorer.com
under Perfumer's Page in a few days after it's published by Qondio which gets first dibs with it.