Twitter should really have some kind of policy for releasing the names of completely unused accounts.
Of course, direct messages also come into play.
"If a username you would like is being used by an account that seems inactive, you should consider selecting an available variation for your use on Twitter. In general, adding numbers, underscores, or abbreviations can help you come up with a great available username."
Every time I read this page, (I checked it a few times because @timothee is taken but has never been used) I'm amused by the "if blah blah…, we offer no solution. But here's a 'solution' that we'll tell you is even better even though it's clearly not."
I can see an argument for not deleting inactive accounts in case their owners want to resume using them, but for accounts that are both inactive and practically unused (the two accounts I've mentioned... the one tweet, and the one reddit comment, both read "hi" - different person, though), they should be freed up.
It's basically the same issue as domain squatting, except that a.) there's no cost involved to help limit it and b.) it can, and is, done by mistake by many people
My preferred Twitter name:
2 Tweets, 1 Following, 0 Followers, inactive for 2 years.
Worse:
I share a pretty unique given name with a world famous musician. That name is taken for everything, always. Even if it wasn't it would likely be stolen from me via some kind of crazy infringement claim.