[development] How to manage major release upgrades of contrib modules?

[Justin Ellison]

Hi listers,

I'm coming up on alpha/beta testing version 3.0 of
http://drupal.org/project/node_gallery, and it's a complete overhaul
of the 2.x branch.  While image/gallery data will not be lost, there's
a good chance that some user customizations with views, themes, etc
will stop working as intended.

I"m scared that the moment I mark 3.0 as the recommended release, I'll
have a stampede of angry users lighting up the issue queue with
"Upgrade to 3.x broke my site!!!".  I'm shipping default views so that
the users have a good starting point, 3.0 will ship with an
UPGRADE.txt file, and we'll have handbook pages in place to explain
things; but is there a best practice for letting users know in advance
that they need to test this upgrade?  Maybe I could release a
recommended release of the 2x branch that implements hook_update_N()
and spits out the contents of the 3.x UPGRADE.txt file?  That wouldn't
catch everyone, but hopefully lessen the impact.

I'd love input and/or examples on how best to deal with this.

Justin