Typhoon Ketsana struck several Southeast Asian countries leaving hundreds dead and millions homeless. It triggered the worst flooding in the Philippines which affected 3 million people  as of this writing. It displaced hundreds of thousands of residents in central Vietnam, Cambodia and southern Laos .
“Ketsana” destroyed more than 300,000 homes , schools and other structures in Vietnam:
Since the ferocious storm struck the central coast on Tuesday, it has killed at least 92 people, left 19 missing, and injured 199, according to the latest statistics from the national flood and storm control committee.
Floodwaters from the torrential rain accompanying the ninth storm from the East Sea this year have submerged or destroyed nearly 337,000 homes, schools and other man-made structures.
It also forced the evacuation of more than 350,000 people :
The storm destroyed or damaged nearly 170,000 homes and flattened crops in six Vietnamese provinces, officials said, while more than 350,000 people were evacuated from the typhoon's path.
Residents describe  “Ketsana” as “the most serious typhoon that’s hit here in four or five years.” They also fear that the “floods could reach the historic highs of 1964.”
Twitter reactions in Vietman about the storm:
jjlechau : Despite Typhoon Ketsana hitting central Vietnam, the southern part remains eerily calm. Just cloudy and a little windy.
quangdieu911 : Storm devastating Quang Nam, Quang Ngai, do something good for they, please… South Vietnam is raining allnight, can't go anywhere in SG.
EmilyPham : The storm that brought heavy flooding to the Philippines, now ugraded to a typhoon, has battered Vietnam.
sereneyee : @mykelism Ketsana hasn't been to visit on this end yet. For now, it is state emergency at the central provinces of the country.
“Ketsana” also pummeled Cambodia which led to the flooding in many areas. Cambodia Calling notes that this is the first time that floods have been so bad in Siem Reap :
…it is the first time the floods have been so bad in Siem Reap.
The floods near the Siem Reap International School were bad and Thyda had to get off her motocycle and push it for 500m. Water got into the engine and it wouldn't start. She said the cars drove fast because drivers did not want to get stuck in the waters. When that happened, the ripples made it harder to push her motocycle.
Andy Brouwer  mentions other flooded areas:
Overnight rain in Siem Reap has left the old market area under water including pub street and other areas including Wat Bo road and the roads in front of Hotel De La Paix, Amansara and La Residence Hotels. National Road 6 out towards the airport is also under water. In Angkor, the roads around Prasat Kravann and Banteay Kdei are flooded and the level of the water in the moat surrounding Angkor Wat is at its peak. At the moment Phnom Penh hasn't really been affected.
Church World Service lists the urgent supplies needed by Cambodians  in evacuation centers:
Church World Service Cambodia reports that in one province, Kompong Thom, 223 villages–some 14,744 families–have been flooded out.
CWS Cambodia has conducted assessments and reports first priority needs in affected regions include food, shelter (plastic sheeting to protect family from the rain and heat), clean water, mosquito netting, and water and sanitation unit
The southern part of Laos was damaged by “Ketsana.” There is widespread flooding  in Xekong and Attapeu provinces. Authorities also reported that 50 hectares of agricultural land is flooded.
Accoridng to KPL Lao News Agency :
Road No.16 , bridges, villages, communication and electricity systems were cut and flooded immediately by the overflow of the Sekong River in Sekong Province since Wednesday’s morning.
At the same time, the water level of the Sedon River, under the influence of the storm, further swelled and submerged rice fields and some villages in two districts of Khongsedon and Vapy, Saravane province.
Thailand was not directly affected by “Ketsana” but the typhoon brought some rains in Bangkok. The Bangkok Bugle writes :
It's a wet and gloomy morning in Bangkok as the remnants of Typhoon Ketsana pass over the city.
There's been consistent, but not heavy, rain since around 8pm last night. The small canal in my soi (street) is high but not close to flooding, and my journey to the office this morning was uneventful. There was a noticeable wind in the city yesterday and this morning I'd estimate it is several degrees cooler than normal right now.
Ketsana is a Lao name , and referred to a tree that resembles agarwood.
To read more about the flood situation in the Philippines, Global Voices offers these articles: Flooding documented on citizen videos , Worst flooding  in 40 years, 2.5 million people  affected by flooding.
The Power of Twitter
The role of social media  in aiding flood rescue teams in the Philippines has been cited here in Global Voices. A specific case can further clarify the important role of microblogging sites like Twitter and Plurk in times of disaster.
A Twitter user asks for volunteers  to deliver supplies to a relief center:
RT @tjmanotoc: 300 hard boiled eggs & 20 loaves of bread in Rockwell, Makati need help in delivery 2 Katipunan/Aurora drop-off point tonight
A few minutes later, the tweet received positive replies :
RT @tjmanotoc: Thanks for the RTs and offers. We have a volunteer na to deliver the eggs. :) once again, I love you Twitter