Misconfigured networking can often be the cause of KDE applications launching slowly, or in the worst case not launching at all. Your X-Server has a very powerful client/server interface and is very network aware.

X uses the hostname to create both a unique key for authorization, and to figure out where (via $DISPLAY) to send the actual windows it's drawing on screen. If your computer doesn't know its own name, it will spend inordinate amounts of time trying to look itself up, a fate you can avoid by simply teaching your computer what its own name is.

Check your /etc/hosts file and ensure there is an entry for localhost that looks something like this at the top of the file (after any comments).

127.0.0.1	localhost

You also should add your computer's fully qualified domain name, short name, and its usual IP address if it has a static IP. If your IP address is assigned dynamically using DHCP you can simply use the address for the loopback device.

127.0.0.1	hal.btl		hal 		(for dhcp)
192.168.0.1	hal.btl		hal		(static)

Make sure that your firewall is not so restrictive that it stops packets to the loopback device. For example in iptables if the default rule on the INPUT chain for this device is set to anything other than >ACCEPT this will cause performance problems in X. To check this, you can type in:

%iptables-save | grep lo
-A INPUT -i lo -j  ACCEPT 

The rule -A INPUT -i lo -j ACCEPT should always work, unless there are other misconfigured rules (Such as a DROP on the OUTPUT chain)