1) It does support PEAR, it's listed on http://packagist.org/about-composer

2) PHP5.3, well, so be it. The people stuck in the past are usually not the ones willing to take the plunge into such solution anyway. They can join us when they are ready.

3) Not yet, but we do have some plans for that.

4) You shouldn't commit your vendor dir, you should commit the composer.lock file, which allows anyone to re-install exactly the same version of the dependencies anywhere. And yes this is similar to Bundler as far as I understand it.

5) We also have plans for that, see https://github.com/composer/composer/issues/57 - but this depends on other features that we need to finish first.