With the recent rash of SqueakSource/GemSource server downtime, I've 
bitten the bullet and updated the bootstrap process for Metacello to 
automatically switch to a secondary repository if the primary repository 
is not available.

I also recommend that if you are maintaining a Metacello configuration 
that you update the class-side #ensureMetacello method for your 
configuration to use the primary and secondary repositories for loading 
the ConfigurationOfMetacello. A new version of the #ensureMetacello 
method can be found here (I've also updated the config template):

   http://code.google.com/p/metacello/wiki/EnsureMetacello

If you are interested in using redundant repositories in your own 
Metacello project then you should take a look at this post:
 
http://gemstonesoup.wordpress.com/2010/06/15/metacello-1-0-beta-27-unfurled/

as it describes the steps that you should follow.

Dale