So Rails and Merb are sort of merging in Rails 3.0? Thats how its been described to me anyway. This means that a lot of what made Rails, Rails will now be moved to plug-ins so that it can be more lightweight. HOwever, what are those plug-ins going to be and as a new Rails developer, what are THE must have - and also more mature - plug-ins that a Rails developer should install? Some good examples I can think of might be will_paginate, ruby_prof or sqlite3-ruby.
My understanding is that Rails (3) will still essentially be composed of the framework components that make it up now i.e. ActiveRecord, ActiveSupport, ActionPack, even prototype.js etc. It's just that the internals have been significantly refactored and cleaned up and it will be much easier to swap out components for alternatives. For example, perhaps replacing ActiveRecord with Data Mapper.