As it says on the banner, I try to focus on stuff that is rare and out-of-print (i.e. things that you can't buy new and artists aren't currently receiving royalties for). My hope is that the exposure this site gives to this music will create demand for commercially available reissues, although I recognize that is a long-shot. When something I've posted is reissued, my policy is to take it down.
I recently discovered a couple things I posted have been reissued, so I took down the links to the MP3s and replaced them with a link to the item at Amazon.com. One poster helpfully pointed out that the Merle Haggard Bob Wills tribute has been reissued as a two-fer with It's All In the Movies. Amazingly, the wonderful Rev-ola label has also reissued the Fun and Games album Elephant Candy. I ordered a copy for myself, and I also highly recommend their Merry-Go-Round reissue.
I have been a little more liberal with my holiday music postings (although the vast majority of what I have posted is currently unavailable) because my plan is to take it all down after New Years. Additionally, at some point music from past months will need to be removed to make room for new stuff (I have only 500 MB of file storage, and am not inclined to pay for more). I'm pretty close to my limit now, but once I take down the holiday music I will have some breathing room. But nothing here is permanent, and I think that's probably for the best anyway.
Also, I usually post links to Amazon.com, but obviously I'm not trying to tell you where to buy your music. It's just easier for me to link there. I buy most of my music from my local independent retailer, Zingg Music.