I already love Pandora and it's concept of radio stations based on artists you already like, but Pandora's Streaming Radio App for iPhone sounds even better and yet another reason to get an iPhone.
According to the Wired article, you can bookmark songs to your profile, purchase songs from iTunes or even ask Pandora why it chose a particular song. For those that don't know, Pandora was instrumental in creating the Music Genome Project:
A given song is represented by a vector containing approximately 150 genes. Each gene corresponds to a characteristic of the music, for example, gender of lead vocalist, level of distortion on the electric guitar, type of background vocals, etc. Rock and pop songs have 150 genes, rap songs have 350, and jazz songs have approximately 400. Other genres of music, such as world and classical, have 300-500 genes. The system depends on a sufficient number of genes to render useful results. Each gene is assigned a number between 1 and 5, and fractional values are allowed but are limited to half integers.
When I first read about the Music Genome Project, I was immediately intrigued because it's all about the science behind music. This drove me to try out Pandora right away and I've been very happily using it ever since. That was back in 2003, IIRC.
This all culminates with the the fact that I don't have an iPhone... yet. So far I've put off purchasing an iPhone because I've heard horror stories about at&t coverage and customer service. Besides, I've been with T-Mobile for years and despite experiencing bad coverage where I live, I get great service almost everywhere else and especially in the EU without changing anything on my phone. So I still like the service. And there's always the possibility of still using the iPhone with a provider other than at&t ;-).
I've also been waiting for the 3G iPhone to be released, which is happening today all over the world with major fanfare. It looks like Apple has yet another major hit on its hands.
Update: It looks like the 3G iPhone release has been plagued with issues on the iTunes server-side, though there doesn't seem to be much detail about the issue yet, especially regarding a solution. :-(