The long term impacts of climate change, including sea level rise need to be taken with care. It is important to consider that all these events are probability distributions that is why scientist use scenarios to understand what the impacts could be. The IPCC report published in 2007 is the most reliable piece of literature with regards to impacts. You can find the report here http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm#1

I have not read all the report so I could not tell what the percentage of the earth's land could be flooded, however, I believe vunerability reports are conducted at national or regional level. In some cases these assessments are sponsored by developed countries or intergovernmental institutions as most of the times high vulnerable countries has no resources to do carry out the studies themselves.

Most vulnerable countries are the members of AOSIS (Alliance of Small Island States), LDC (Least Developed Countries) among others.

I found a this report [http://www.maplecroft.com/Climate_change_info.php] on climate change vulnerability, I hope it is useful.

Not sure about the percentage of land area affected by sea level rise, but just imagine: if sea level increases by 23 feet, then you could think that many coastal areas whose level above sea is below that height, may suffer recurrent or permanent flooding. About effects, the problem is that an important part of World's population live in coastal areas. Then imagine a town or a city where part of it is under water, recurrently hit by waves or where tide comes inland during nights, not to mention during storms or hurricanes. The streets, building, schools, farms, ports, markets, etc. will not be useful anymore. New Orleans is an example on what may happen to a city after massive flooding. The state of Tabasco in Mexico lives a similar situation. Coastal areas of Bangladesh, Vietnam and the UK.

What will people and governments do?

As suggested by Joe, read the IPCC report and you will get some ideas of the magnitude.