I've been using Spotify since the early BETA days, and it has changed alot since then, i think 6 months free is perfect as every company has bills to pay.
And i do see it as being quite popular as everyone loves some kind of music, not everyone plays games (think BT's latest offer) so if you look at it that way then it's a great offer.
The 12 month contract is all good as most things these days come with 18 - 24 month contracts so it's not that bad plus this is just a bonus to a great service