Update: Anatomy of a news story - despite about a half dozen sources reporting this, Last.fm chimes in to say the original source, Wired, misinterpreted their comments about an expanded subscription service that's on the way. See the comment thread.
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We'd assumed that Last.fm already had subscriptions, but after a little digging we found that they've stealthily rolled out a subscription service in the past few days (or weeks?), providing ad-free radio for $3/month. This was hinted at when Last.fm announced the partnership with Warner in February.
Benefits include a subtle blue icon to indicate pro status, the ability to broadcast your own radio station to others and the highest priority when the webserver is getting a little busy - free users will be kicked off to make way for the elite. A more extensive subscription service is also being planned said Wired on Friday.