If you want to get version information about a gem the easiest way to do it is with this command

gem list 

For example

gem list activemerchant

will output the activemerchant versions I have installed. You can pass only part of the name like

gem list a

get the names of all gems (and versions) that start with "a". There are a lot more options so here is a link to the gem command reference http://rubygems.org/read/chapter/10

The commands here are useful if you've installed a gem but the version you've configured in your environment.rb file is different. To quickly grab the right version, this command is pretty handy.

Just finishing up brewing up some fresh ground comments...