We use capistrano to deploy our rails applications from a subversion repository that is accessed using svn+ssh.  Recently we ran into a problem where Capistrano was unable to connect to subversion from some of the deployment hosts with an error like:

*** [err :: host.domain.com] ssh_exchange_identification: Connection closed by remote host

Since capistrano tries to fire off N svn checkouts simultaneously, it was running into a connection limit for ssh on the the subversion server.  Turns out there is a MaxStartups setting for sshd_config which effectively determines how many clients can be trying to connect simultaneously.  It defaults to 10, and our failures started happening when we went above 10.  Changing the value to 50 on our svn/ssh server cleared up the problem.