A guide to easily disable IPv6 support on your Linux workstation / server:
1. Add the two lines, if not already present, to /etc/modprobe.conf:


alias net-pf-10 off
alias ipv6 off

For Fedora 7 you should add the command to blacklist instead as shown below:
blacklist net-pf-10
Note: I haven't personally tested on Fedora 7.

Note: Try to copy-paste these lines instead of typing them. I faced problems in one computer after typing it in. It wasn't something which was visible to me on casual inspection but copy-paste solved it.

2. Open /etc/sysconfig/network and look for the line containing NETWORKING_IPV6 and change the value to no as shown below:
NETWORKING_IPV6=no

3. Stop ip6tables firewall:
/sbin/service ip6tables stop

4. Prevent the ip6tables firewall from coming up ever again:
/sbin/chkconfig ip6tables off

5. Restart your network to see if everything is working correctly:
/sbin/service network restart

Some articles suggest rebooting the machine at this stage so you may do that too.

Note: The original information is derived from this article and modified based on my experience with many servers.

Will this improve your performance? I don't have benchmarks but in my experience it does. And for web severs every bit of performance you can extract is worth it. So if you are not using ipv6 then I suggest you disable it.