I feel pretty much the same as sincere on this issue - ever since I've showed off some of the conversion work I'm doing for my own personal collection, I've had quite a few people contact me about them, but that's not the problem. The problem is that many of the people are asking me to send them mp3s of my rips. If another DJ asks me and he has some stuff I can use for a set or project, then yea, I may do an mp3 swap, but other than that, there's not much point, imho.
I prefer originals, primarily because the quality of mp3s just isn't as good as a retail CD, cassette, or vinyl records.
On the other hand, I have some people who actually send me physical copies and want me to rip them to mp3 for them (usually just tapes or records, but I've received a few CDs too, since I scan the artwork in HQ and some people just include them with the other stuff). Since I live in a recording studio, I have all the necessary equipment to do all these things "right", and tape rips seem to go horribly wrong for many people without experience (and/or good equipment). I know a lot of the ones I do will end up on different websites, as some of the people sending stuff are doing it only to share on said sites, so that way they can trade those with others or what not. I have some people that ask me to rip everything I put up on ebay, even if it's only $2!
I feel that many mp3 collectors I've met don't really care about the music. They really love some of it, but there's no reason to have 750,000 albums archived on your hard drive if you're NOT a DJ (or even if you are a DJ). I've met people who hoard mp3s like every physical copy was burned, and they still don't even listen to half of what they download. Admittedly, I've got a few records I've never gotten around to spinning, but not a whole lot.
So I guess I'm a little in-between on the matter, since I'm somewhat of an enabler... but as far as my own personal collection and practices go, I don't share the stuff that took me years to find, unless there's significant reason to do so.