I upgraded from Kubuntu 8.04 to whatever the latest version is, 9.04 I think. I just checked ksysguard just out of curiosity. It says 100% CPU load. The process known as kded4 uses between 70 to 90%. What is up with that? My system doesn't feel slow but I don't like the idea of a process that keeps the CPU active.

Lots of reasons for high cpu usage, you can research here:https://bugs.launchpad.net/bugs/+bug....scope.target=
for users reporting similar.
for comparisons............

Host/Kernel/OS "wirechief-laptop" running Linux 2.6.30-020630rc2-generic x86_64 [ Ubuntu 9.04 ]
CPU Info (1) Intel Core2 Duo T7300 @ 4096 KB cache flags( sse sse2 nx lm pni vmx ) clocked at [ 2001.000 MHz ]
(2) Intel Core2 Duo T7300 @ 4096 KB cache flags( sse sse2 nx lm pni vmx ) clocked at [ 800.000 MHz ]
Videocard Intel Mobile GM965/GL960 Integrated Graphics Controller X.Org 1.6.0 [ 1280x800 ]
Network cards Broadcom NetLink BCM5787M Gigabit Ethernet PCI Express
Intel PRO/Wireless 3945ABG [Golan] Network Connection
Processes 156 | Uptime 1:18 | Memory 683.3/1977.7MB | HDD ATA HITACHI HTS54161 Size 120GB (7%used) | Client Shell | Infobash v2.67.1

cat cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 15
model name : Intel(R) Core(TM)2 Duo CPU T7300 @ 2.00GHz
stepping : 10
cpu MHz : 800.000
cache size : 4096 KB
physical id : 0
siblings : 1
core id : 0
cpu cores : 2
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 10
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm ida tpr_shadow vnmi flexpriority
bogomips : 3989.96
clflush size : 64
cache_alignment : 64
address sizes : 36 bits physical, 48 bits virtual
power management:

processor : 1
vendor_id : GenuineIntel
cpu family : 6
model : 15
model name : Intel(R) Core(TM)2 Duo CPU T7300 @ 2.00GHz
stepping : 10
cpu MHz : 800.000
cache size : 4096 KB
physical id : 0
siblings : 1
core id : 1
cpu cores : 2
apicid : 1
initial apicid : 1
fpu : yes
fpu_exception : yes
cpuid level : 10
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm ida tpr_shadow vnmi flexpriority
bogomips : 3989.98
clflush size : 64
cache_alignment : 64
address sizes : 36 bits physical, 48 bits virtual
power management:

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I'm not sure what happened but today, the CPU is normal. Well actually, it is 10% with nothing running on my AthlonXP 2800+

If it was there for a while and went away the following day, and there was much disk activity, probably just something indexing your disk (updatedb, beagle and rather too many others).