We use Team City for Continuous Integration. For a rails app its definitely a good setup and for free hard to beat. I'd never used it before but given the quality of Ruby Mine it certainly seems to hold up to that standard. I've been reading a lot about Jenkins in the past few months and set that up for a project but it seemed to be missing a few options I was used to in Team City. I couldn't seem to get the options straight for bundler or gemsets without a fair amount of custom changes.
Using the Engine Yard gem and deployment, no issues, but switching over to capistrano deploys, a compounded problem for automatic deploys to staging.
The first step is to get the deployment working command line. SSH in to your CI server and drop in to the build agents work dir and run the cap.
The catch for the next part is that Team City doesn't load an environment when running a build. This means no environment variables. Normally you might not need to worry about this, but when you are using Net:SSH as capistrano does, along with agent forwarding you'll end up with some issues. Googling around this most people seem to suggest just copying your private key to the remote server. This means the forward agent is no longer needed but now you have your keys to the castle on your staging server - not a good idea.
When prompted save the key to a safe place or just drop it in to ~/.ssh/teamcity and don't specify a passphrase, just hit enter when prompted.
$ ssh-keygen -t rsa -C "firstname.lastname@example.org"
Git Project Page -> Admin -> Deploy Keys -> Add Another Deploy Key
Host example.domain.com HostName example.domain.com IdentityFile /path/to/ssh/key/teamcity User deploy Host * ForwardAgent yes
ssh-agent -a /tmp/ssh-teamcity/agent
Edit your project configuration on step 6 - Properties and Environment Variables.
Set HOME to your HOME dir
Set SSH_AGENT_PID to the agent PID
Set SSH_AUTH_SOCK to /tmp/ssh-teamcity/agent
Setup a new command line build step to add the key to the agent
Command Executable: /usr/bin/ssh-add Command parameters: /path/to/ssh/key/teamcity
Setup a new command line build step to deploy
Command Executable: cap Command parameters: staging deploy