My $0.02:

I think raa-install is excellent and I use it regularly. I have no 
opinion about YAML or REXML because I've never used them. I have 
nothing against petitions. I trust Matz's judgment and that of the 
ruby-core team.

I just don't think that the problem space is sufficiently stable to put 
a package manager in the standard library -- which, by the way, is not 
a criticism of raa-install or anyone else.

Regards,

Mark Wilson