So the point of view on SC matters. 

If you live the EL/EPEL world and have some Fedora, SC make a lot of sense.  If you only use Fedora, Fedora moves fast enough to likely not have a ton of use for them.  I think that's been hit.

As for Puppet, I've proposed several ideas on how to improve Puppet on Fedora/EPEL and basically it turned into a bitch-fest. I'm still working a plan on it.  When a distro chooses "First" as one of their foundations, that comes with problems.  Fedora is the first (and only of the 8 major Linux distros we support) to only have Ruby 1.9 support.  We have a puppet that fully supports Ruby 1.9.  It didn't make it into Fedora 17.  I've been working hard to see if it's possible for F18.

I could get into more discussion on Puppet with EPEL/Fedora, but that's been covered. 

Back to software collections: I'm in favor for EL.  On Fedora, meh. In fact some of CentOS people have already spoken with Puppet Labs about maybe doing something with SCs for EL if needed. 

(Obvious disclaimer, I work at Puppet Labs)