I've just found a nice article about enabling DNS-Cache for Konqueror at fedorawiki.de. It's very useful, because Konqueror doesn't provide this feature. If you take e.g. the german freemail provider http://gmx.net, Konqueror sends a huge amount of dns queries to load all the pictures and stuff. You really notice the performance gain if you cache these queries with a local DNS server, for example dnsmasq.
Here are the steps to install and configure dnsmasq: