Age - 49.
New stuff - definitely a no-no. Give the bands a chance to sell some first ferchrissakes! If you have a blog and think you are doing this to help promote a band, maybe you should consider giving a link to their myspace or facebook instead. Most bands have enough full length songs on there to make a judgement call on whether their album is worth buying.
Downloading for a "taste" - nice theory and I'm sure some people do that and then go out and buy, but my gut feeling is that percentage is low. If blog owners really want that to happen, then why supply the mp3s in quality that's good enough to burn to CD? If the mp3s were provided in, say, 64kbps quality, people could still hear the album but wouldn't be tempted to burn and keep it 'cause the quality would be poor.
Really old music - jazz from the 30s for instance, stuff that would be out of copyright anyway I don't have so much of a problem with.