Everything seems to be deprecated in Rails 3

I've just built my Rails 2 app, and then it turned out the hosting provider had upgraded to Rails 3 and had dropped Rails 2 support completely.

So, I've decided on converting my app. It's not a pretty thing.

• Everything seems to have been deprecated or entirely moved out. I am constantly getting warning messages that I shouldn't use this or that.
• I am wondering pretty much at the moment why do I have to explicitly require files all over the place?
• f.error_messages has been deprecated and is now a plug-in.

Not to mention a 'welcoming' message in the Getting Started with Rails guide:

Note that Ruby 1.8.7 p248 and p249 have marshaling bugs that crash Rails 3.0. Ruby Enterprise Edition have these fixed since release 1.8.7-2010.02 though. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults on Rails 3.0, so if you want to use Rails 3 with 1.9.x jump on 1.9.2 for smooth sailing.

I hope it'll all work in the end.