A bit of history: osx [0] and windows [1]

IIRC most issues revolve around plugins and performance (notably V8), possibly not directly because of type sizes but similar low level stuff that hampers JS-to-the-metal optimisations.

Still waiting on OSX though.

[0]: https://code.google.com/p/chromium/issues/detail?id=8606

[1]: https://code.google.com/p/chromium/issues/detail?id=18323

Linux, MacOS, and nearly all other Unix-y things use LP64 (int is 32bit, long is 64bit). Windows x86_64 uses LLP64 (int is 32bit, long is 32bit). This can make porting a pain.