integer datetimes

Has any thought been given to making integer datetimes the default on 
platforms that support it? Are there any performance implications? I saw 
the Tom Lane raised this when it was added, and it looks like the 
decision was deferred. I know that, ceteris paribus, I would rather have 
fixed microsecond precision across a slightly smaller range in every app 
I've ever worked on. Which platforms don't support it? I did some search 
on all these questions but didn't find much info. I'm probably going to 
add the flag enabling it to the default buildfarm setup.

cheers

andrew