First, some defenitions...
We must define what we're talking about here.
Spyware: Software that records various things you do on your computer, and reports them to someone else.
Adware: Software that causes ads to appear on your computer, or changes the way your computer works to force you to see ads or website you did not request.
Spyware is a very general term, that can include legitimate tools used by companies (keyloggers, for example.) The 'legitimate' kind exist for OS X. The less-than-legitimate kind (ones that are put on your computer by advertising companies to track your browsing habits,) are non-existent on OS X.
Adware is more specific. It, by definition, is software from advertising companies. None of this exists (to my knowledge) for OS X. I'll have to research the iTunes plugin for Konfabulator, but this is the first I have heard of it being called adware.
In the Windows world, both of these illegitimate kinds are sometimes referred to generically as 'malware'. It's a big problem on Windows. I figure it's only a matter of time before we see CoolWebSearch, Alexa, or Gator on the Mac.