What are the security implications of doing this? I have a form on my localhost machine which I fill in and then this data gets submitted via POST to the live server, where it is run as a mysql query to update the live database. This is currently the easiest way for me to keep both local and live databases in sync. Should I look to md5 the data or anything like that, or is it OK the way it is currently?
How would "md5"ing the data work exactly? md5 is a one-way street; it's only useful if you never need to see your data again. As for your main question, it depends on the integrity of the path between your machine and the live server. In your position I'd probably create a self-signed SSL certificate for the live server and install the fingerprint on the local server. Then they can communicate securely.