"Every public tweet, ever, since Twitter’s inception in March 2006, will be archived digitally at the Library of Congress."That's right... every thoughtless, trivial, and crass remark you ever tweeted is now going to be made available for future generations (your tax money at work ).
This is actually a very positive development because this corpus of short messages will provide invaluable to researchers and historians. My guess is some research on this corpus will likely be used to improve web search. I will certainly have my web IR course in the spring do some analysis on the corpus.
My hope is that some day the LoC will also archive all of Facebook. This will prove much more problematic as Facebook data is inherently private, and access to the archive will likely need to be restricted. But losing this treasure chest of bytes would, in my estimation, be far more of a loss to society and future researchers than losing a few tweets.