One minor hitch: SvnX can't log into a server that uses svn+ssh as its access method if ssh requires a manually typed password.
The work-around is to establish a private/public key pair for ssh. Once you do that, keychain will offer to store the password, and SvnX can function normally.
In theory sshkeychain should let the key chain remember plain passwords, but I couldn't get this to work on 10.6.
The keypair can be established as follows:
ssh-keygen -t rsa
(type desired password, accept default file name)
scp id_rsa.pub email@example.com:/home/you/.ssh/auhorized_keys
(where "you" is your unix login name. authorized_keys may need a different name for different servers.)