I don't trust this sort of thing at all. The need for warrants was intended to stop this sort of thing; if it was supposed to be "ok" to invade people's privacy like this, we'd never use warrants. Here are some reasons they might be nefcessary (though these have been hinted at already):
1) Discrimination. If the government findss that you have a certain lifestyle (eating habits, excercising habits, sexual behavior, whatever) that they don't like, it could very well be possible for them to discriminate against you in a job where such factors should not be an issue. Above that, if this information is unclassified, not only does the government know about it, but so do all your future employers, employees, etc.
2) Despotism. If the government finds that you do not support those in power, who's to say they won't use the same discrimination as above? Above that, they could stop you from assembling with like-minded friends (even if it is for peaceful discussion) to stifle any activity that isn't pro-government. This has some serious consequences; newspapers could be forced to print pro-government propaganda, opposing political parties could be eradicated, even something as peaceful as this forum could be stopped.
In addition, the United States does not have a history of only arresting "the bad guys". We arrested some people in the middle east for as little as wearing a Casio watch or a drab jacket (
http://www.msnbc.msn.com/id/11674324/)
Given this information, I don't think it's safe at all to trust the government to have wholesale access to private information.
In addition, AT&T might not have just provided phone records. AT&T possibly diverted wholesale domestic communications to the NSA by splicing the signal from their fiberoptic cables into a "secret" room where people from the NSA did installation of...something, according to a retired AT&T worker (
http://www.wired.com/news/technology/0,70619-0.html