Not only will they be able to listen to music that I like, they might be able to download MySQL as though they were me or comment on Engadget articles as me.
None of which are particularly concerning. Because those are throwaway accounts for me.
Make sure you've got a process in place to at least semi-regularly audit your list of "throwaway accounts".
A long time ago, I signed up to PerkMonks for some unimportant reason. Since it was unimportant then (and still is now) I used my then-standard "throwaway login". Sometime later, and before it became "a thing", I signed up for this new "microblgging service" using my "throwaway login" - it was called Twitter - nobody much had heard of it back then. Fastforward 3 years or so… Twitter had become, while not _important_, at least a place where I consider my personal reputation is important. Shortly after the PerkMonks user database got exposed (with it's cleartext passwords! facepalm!), I got an early morning text message from a friend "Acai berry spam from your Twitter account! Ha ha!" (Thanks Colin… For both the heads-up and the deserved ridicule)
If you're using the same "throwaway" credentials in a bunch of places you consider "unimportant" - make sure you upgrade those to properly secure credentials when the importance of those places changes.
Or better still, get 1Password/KeyPass/LastPass/WhatEver and stop doing that…
Not only will they be able to listen to music that I like, they might be able to download MySQL as though they were me or comment on Engadget articles as me.
None of which are particularly concerning. Because those are throwaway accounts for me.