Each few weeks I try to put together a mix tape (actually a cd) for my girlfriend as we both like the same music. Sometimes I wander around with some music playing and realize: 'this is something she might like'.

Before RTM it mostly ended right there; not having something to write at hand, and consequently forgetting all about the song. Now, I just put it into my Mixtape list on Remember The Milk on my Android phone; so at home I can easily find what songs I still need to add.

Previously, I needed to have some hours specially for listening to long lists of tracks at home. Now I can do most of the music listening on the go (where I usually listen to most of my music anyhow) and just put together the final product at home.

Not that much of a usability hack, but it really made it much simpler to put together that lot of music each few weeks.