Back in October Subsonic was updated with a Holo interface, which was a vast improvement over the old UI. However, that update also included ads. There was a $4.44 in-app purchase to remove them, but now that's a thing of the past. The new version of Subsonic for Android is completely ad-free by default.
The upsell in the app didn't really make much sense in the first place. Subsonic is a streaming service that runs from your home PC to give you access to your media on the go. However, the server software is not free if you want to stream to a mobile device, so charging again in the app felt a little unnecessary.