Something I haven't seen mentioned elsewhere.
The way Twitter packaged up the archives that people are starting to download enables new kinds of apps to be developed. That's because the data files are distributed in a very software-readable format called JSON.
It will be possible to make all kinds of interesting tweet-browsers without hitting any rate limits, because you won't have to access twitter.com to get at all your tweets.
One thing they haven't said is how frequently they will allow people to download their archives. Once a week? Once a month? Or is it a one-time thing?
But this is important. It will make a pretty substantial difference in the tech market, imho.
If I had access to my own archive I would start playing with this right away.