Why is this such a big deal? If Twitter was originally built with a signed-32bit integer as their tweet primary key, then we can say at least one or more of the following:

a) Twitter never expected to get this big
b) The developers lacked the knowledge/foresight/intelligence to at least used an UNSIGNED integer as their primary key
c) The developers were too cheap to spend the extra 4 bytes of disk space per tweet to make the primary key 64bit

Are you certain of that? It could be a 32 bit unsigned integer. Or if Twitter is running on a 64 bit operating system, the theoretical limit will be reached some 2 BILLION years from now, assuming the same rate of growth.

So you make one unique identifier for the user, and another for the post of that user, thus exponentially increasing the limit, it's easy. There are actually hundreds of different ways of dealing with this problem.

This, is just a publicity stunt. People will join, and post, to try and "crash" twitter, but it will never happen, and their user base will increase.

Twitter's not going to be setting status_ids to negative numbers. As Matt Sanford, a Twitter API developer, has said:

"There is no change to the format of responses and the number will continue to grow upward."

Some clients that cannot properly interpret 32-bit signed ints so large will have an issue with negative numbers.