Richard Stallman about that very topic.
This can be dangerous for the same reason Twitter's per-country censorship is dangerous.
EFF: What Does Twitter’s Country-by-Country Takedown System Mean for Freedom of Expression?
For now, the overall effect is less censorship rather than more censorship, since they used to take things down for all users.
Now, however, there is nothing to discourage Twitter from opening an office in Turkey and censoring people there, opening an office in Thailand and censoring people there, and opening an office in the next Egypt and censoring people there.
The one common defense for these moves is that sites have to abide to local law. I don't really agree that much. I don't think it is proper to abide to laws that are not fair. I also think that twitter/google could just avoid to make new offices in countries that force them to censor.
Note, however, that this is nothing new once we remember that google's search has been doing this in China for years.
Speaking of censorship, please do remember that we are back to the age of library burning.
Megaupload's Innocent Users Deserve Their Data Back