Interesting post on this – plus pictures of the raised Cheonan. HT: Information Dissemination.
What is interesting is that the ship was split in half!
South Korea has now publicly announced that the Cheonan was likely hit by a torpedo: see this NY Times article.
As Rob has noted, “War is simply not in South Korea’s interests.” So, I’d like to see some public opinion polling to see if the government will be pressured to take a more bellicose stance. War of Jenkins’ Ear anyone (a case in which, according to some, public opinion pushed the government further than it may have wanted to go)? I doubt it.
Update: Will the new rallying cry for the South Korean Navy be: “Remember the Cheonan”?
PILEUS 
I’ve been reading a bunch of English language Korean websites and a Korean friend has read some in Korean for me. They all have editorials that basically end: If it can conclusively be shown that NK was responsible a strong response (whatever that may be; they don’t ever say) is required. Anything less will harm the government badly.