The basic gist of the site: visitors may access music, video, photographs, blog posts and polls. However, if you want to comment, rate, tag or the post of new content, you have to register an free account. A key feature is the media playlist where content posted from multiple sources may be collected into a playlist which itself may be published for comments, tags and rating. Playlists can consist of videos, music or images. I’ve never used it but there is the 'Remix Player,' where music and images may be combined into a single presentation with customizable image transition effects.

(side note: yes, I am listening to Michael Jackson. Listen to the Essential Michael Jackson album playlist. Wonderfulness.)
Pros: listen to complete albums, peruse playlists by listeners with similar tastes, make your own playlists without having to upload content, skip songs without limit, opportunity to buy songs off of the site.
Cons: selection of mixed playlists is dependent on popularity of artist (less known artists simply have their album playlists due to fewer users making own playlists), small number of songs are previews only lasting 30 seconds, occasional :15 second commercials.
Overall, I love the site. Any individual that has the faintest hint of music ADD will love it more than their Pandora stations. Check it out: http://www.imeem.com/