Dan Rather Offended

Dan Rather is suing CBS. I must admit, I didn't see this one coming. I thought if he'd lash out in defense of his reputation, it would have been sooner. This one bubbled up unexpectedly.
At issue is a story CBS did on President Bush's service (or lack thereof) in the National Guard during Vietnam. Documents upon which the story was partially based were later deemed unverifiable, at best. An external investigation ensued, and Rather later retired ("in disgrace" would be too strong a term but certainly not with the acclaim one would have expected before the Bush story).
Is the suit worth it? Was his reputation damaged and if so, can he rebuild it by a suit like this? Does he damage his cause more by bringing the issues up again? What obligations do the news media have to verify information provided by a source?