OK, given that there are a wide range of opinions about the various music services, I decided to sign up for them and find out what they all look like and are about.
My preliminary results are in the table on this site.
Feel free to add your comments by commenting on this article.
Interface-wise, Rhapsody is the prettiest, but iTunes still wins in my mind for the most navigable. Pressplay's client's UI is over-tabbed and under organized, making it the big loser as far as I'm concerned.
Installation of Rhapsody and iTunes were easy. Pressplay's WMP installation failed after 5 minutes on my XP machine with plenty of: CPU, RAM, Disk.