No other accounts, personally. Always seemed like too much work.
As for others that might share the same IP as me while posting, lets see...everyone that posts from my office buildings where I work. NAT works like that. Also, anyone in my area who might pick up my dynamic comcast IP. Plus, at least one of my players has an account here(name unknown), and he probably posts on the laptop he brings, and hooks up to my wireless. And for fun, I sometimes post off my phone, and the 3G network also uses dynamic IP addresses.
BTW, since IP matching doesn't significantly impact things like multi-ing in games, and tends to do annoying things to the player base due to, yknow, the internet working that way, why would a web forum be any different?