Originally Posted by Wildhoney

Trouble is with the IP address is that some ISPs, such as AOL, their IP changes on every page request and so any end-user on your website using AOL, or other ISP that go down the same route with their IPs, would be required to login in every single time.

Moreover, for your passwords you'll no doubt be wanting to apply a salt to them and then MD5ing them together.

Working with Dynamic Cryptography Salts
Cryptography's Sodium Chloride