I'm mentioning tuning your SSL ciphers a number of times in this thread. It really is quite important. For Nginx you should compile it with the latest OpenSSL (1.0.1e right now -- you can statically link it if you dont want to mess up your OS's packages) to get the latest ciphers.

Use a config line like the following in nginx:

ssl_ciphers ECDHE-RSA-AES128-SHA256:AES128-GCM-SHA256:RC4:HIGH:!MD5:!aNULL:!EDH;

RC4 is a problem right now but unfortunately there's not a good solution until we get more TLS 1.2 support out there.

If you don't do this sort of tuning you're exposed to some weak ciphers that can result in attacks.