I pronounce it DAY-mun when speaking to other UNIX hackers and DEE-mun when speaking to windows users or regular users. I've never been formerly told how to pronounce it when I started hacking in Redhat. Since most early hackers were smarter than most I assumed there was some sort of word trickery involved (met another guy that pronounced it DAY-EE-mun) that would make me stick out like a newb.
I've known for a long time how it was meant to be pronounced, so when talking to other programmers/hacker types, I say DEE-mun, but when talking to ordinary people I say DAE-mun so they don't say "wtf demons on computers now?" or somesuch - most don't, but some more religious types look at you funny...
Unfortunately, the Classical Latin pronunciation is not used colloquially, so in everyday life, I must stray from what I learned, lest I be viewed as the incorrect one.
http://dictionary.reference.com/browse/daemon Pronounces it DEE-mon which is how I've always said it. (The Golden Compass audiobooks and movie also pronounce their spirit animals, called Daemons, as DEE-mon).
I always thought the UNIX term came from the meaning of a subordinate/helper spirit (which is what they are, basically - helper services)
As an authority on the subject, I submit that since "Damon" is pronounced Day-mun, that "daemon" must be pronounced Dee-mun, as it's just an alternate spelling of "demon".
But mostly I just want to stop being confused whenever someone says "daemon" around the office, and I think they're talking to me.
Typically in English, an e after a vowel indicates the vowel should make a hard sound rather than soft. So looking at it that way, Daemon should have a hard a (like the name of the letter), thus DAY-mon.
Also: I pronounce "daemon" as "DAY-mun," as opposed to "demon", which I pronounce "DEE-mun." Do the rest of you make this distinction?