If someone is monitoring all of the traffic on a network, and then I connect to it, and log into a website that is protected with SSL - is there any security risk?
Some, but there is risk everywhere.
Extra diligence is required, however, to ensure that your certificate is valid.
Never accept a self-signed or expired certificate in this scenario(you'll see security warnings from modern browsers). Click on the lock next to your URL to ensure everything looks good!
Ensure the the site is using complete SSL and not mixed mode(Some elements encrypted others not or login via HTTPS and pop back to HTTP after) and you should be alright to use it.
If you haven't pruned the CA root list in your browser then you shouldn't feel great about having privacy from government entities - otherwise if your system is patched/current and so is the sever's and you are doing reasonable validity checking (expiration, chain validity, certificate status) you are probably in reasonable shape against unsophisticated attackers.