As I was a Beta tester of Spotify in its early days I have enjoyed unlimited music (All be it with adverts) but have been told I will also have the hours on my account slashed from Unlimited to just 10 hours, Ouch!
therfore I have been left with no choice but to subscribe to spotify unlimited giving me advert free unlimited playtime music, which is still a vary good deal at £5 a month, Its £10 a month if I want to sync the music to my phone and get early access to new tracks, but the £5 service is all I need for now.
When I get a new smart phone I may concider the premium service to have music on my phone.
Spotify is a great free alternative to Ilegally downloading music, and when it launches in the States I encoutage its use, its really easy to find music, you just type a song name and in seconds you have it playing. There is an advert every like 4-5 Song, usully spotify premium, the portal 2 advert had been playing loads, but i just subscribed to Unlimited so no adverts for me. All the Adverts are Audio adverts, sometimes with a Picture that appears on a sidebar in the spotify player, nothing intrusive really.