I've been running 1.2.3 for a long time and just the other day installed 1.2.6 to prepare for an eventual upgrade to 2.x. While I was at it, I installed 2.0.2 which I plan to use for a new app I'm writing. I figure it will be less painful to learn about 2.0 in a new app and then upgrade an existing one (since the existing one will be in production when I upgrade it). So after installing the new gems, I changed environment.rb to RAILS_GEM_VERSION = "1.2.6", and I also had to change a couple of require_gem statements to gem in boot.rb. Everything seems fine so far.
I just (10 minutes ago) saw someone reference rake rails:update which, I suppose, one should run after updating an app to a newer version of rails. Can a version number be passed to that rake task or does it update to the latest installed version? Or will it use what's defined in the app itself? I wouldn't want my 1.2.6 app upgraded to 2.0.2.
BTW, I guess I'm only concerned about this in case there are other config/system files out there that need to be update, primarily the require_gem/gem situation. And there might be other things that I'm not aware of.