My brother-in-law has been on me for a while now to convert to RVM.  For those who don't know, RVM is Ruby Version Manager.  It makes switching back and forth between different versions of ruby and different gemsets a piece of cake.  Here are a few tips I learned while setting up RVM on my linux box.

These are in no particular order.

1.  If you don't use bundler start.

2. Install bundler and passenger to the global gemset.  

[code] rvm use 1.9.2@global gem install bundler passenger [/code]

3. Add config/setup_load_paths.rb to your rails 3 app or to your sinatra app to make passenger see your gemsets.  Then add the following to that file, courtesy of my brother-in-law.  The key here is that it works for sinatra too.  Took me all day to figure that out. :)  (Rails is now Rack based.)

4. For Passenger, once it is installed in the global gemset, you can setup as normal.

5. This is a good resource for item 3.

6. It is possible to have a default ruby version and gemset automatically load when you change into a directory.

Add .rvmrc to the directory.  

[code] touch .rvmrc [/code]

Create a gemset for the directory.

[code] rvm gemset create <name of gemset> [/code]

Then place the following code into the .rvmrc file.

[code] rvm use <ruby version>@<name of gemset> [/code]

7. Don't forget to switch back to the ruby version/gemset you really want to use if you don't have .rvmrc files.

I will continue to add to this list if I think of more useful stuff.

RVM is easy to install, and easy to use.  Don't be afraid.  Go, now, do it.  See what its all about and save yourself some ruby headaches.