There's some natural and unavoidable latency due to ssh/smb/ftp/whatever you're using but I use tramp daily and in practice it's quite unnoticeable. Local machines respond immediately, machines in the same country are very much usable as well.

Just make tramp keep the connections alive longer and cache the password. And set backup directory to something local!

C-c C-s is still faster than using a shell in another console and scp/rsync.

It's a tradeoff - it might be a little bit slower in opening a file, but then you get to edit it locally, which can be way better than using an editor on a remote machine through a slow link.

my experience tells that over ftp it can be very slow, but over ssh it is fine.

I was referring to ssh.