The Hype Machine and Tumblr are two different takes on the same idea. Build a music service around the music people blog about.
At the Hype Machine, they crawl blogs that are known music blogs and pull the songs onto their service and showcase them. I am constantly finding new music via the Hype Machine.
Tumblr is not a music service per se. It's a blogging service and our firm has an investment in it so I have a vested interest in its success. Tumblr does three important things with it's service that makes it unique in the market;
1) it encourages short posts (not twitter short, but shorter than what you'd find on wordpress or typepad)
2) the blogger categorizes the post by media type (audio, video, photos, quotes, links, text, etc)
3) it encourages reblogging which is autoposting another's post to your blog
I think the act of reblogging media (audio, video, photos, quotes, links) is a very powerful form of curation and you can find all sorts of amazing curated blogs on tumblr.
All that said, Tumblr is a few features short of being a killer music blogging service. For start, if you go to Tuneage or The Music, two of my favorite music reblogs on Tumblr, you can't "play" the blog. What I want is the ability to simply launch a player and listen to the blog in reverse chronological order with skip and reblog built into the player.
One of the great things about Tumblr music, and something I've mentioned in the past, is you can only post one mp3 per day to Tumblr. The one a day thing is really a big time quality filter and is one of the main reasons I like to listen on Tumblr so much.
Another thing I'd like is the ability to create curation pages on Tumblr, one for music, one for photos, one for videos, one for links, one for quotes. I don't want to reblog every thing I find on Tumblr to my main page but I would like to reblog to these themed pages. It would be like my "loved page on hype machine".
I hope that David and Marco add these features soon. It will make listening on Tumblr even better than it is already.