[CentOS] High system load but low cpu usage

I'm trying to figure out what's causing an average system load of 3+
to 5+ on an Intel quad core. The server has with 2 KVM guests
(assigned 1 core and 2 cores) that's lightly loaded (0.1~0.4) each.
Both guest/host are running 64bit CentOS 5.6

Originally I suspected maybe it's i/o but on checking, there is very
little i/o wait % as well. Plenty of free disk space available on all
physical drives and memory sufficient for the usage with barely any
swap in use.

While performance/responsiveness of the host and guests doesn't seem
to be affected, I'm still concerned about this odd load figures. Would
appreciate it if anybody can suggest what else I should be looking at?

Output of various commands on the host:

Top
===
top - 15:15:39 up 5 days,  8:48,  1 user,  load average: 4.76, 4.18, 4.43
Tasks: 210 total,   1 running, 209 sleeping,   0 stopped,   0 zombie
Cpu(s):  4.1%us,  2.5%sy,  0.0%ni, 76.4%id, 17.0%wa,  0.0%hi,  0.1%si,  0.0%st
Mem:   3759496k total,  2813076k used,   946420k free,   357300k buffers
Swap:  8193016k total,     5648k used,  8187368k free,   736640k cached

free -m
======
             total       used       free     shared    buffers     cached
Mem:          3671       2750        921          0        348        719
-/+ buffers/cache:       1682       1989
Swap:         8000          5       7995


vmstat 3
======
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 2  0   5648 949072 357096 735788    0    0   105    50   17   22  2  1 95  1  0
 0  0   5648 949428 357104 735788    0    0    44  2682 14142 14697  6
 4 84  6  0
 0  0   5648 949304 357104 735788    0    0     1   324 14047 14753  2
 1 96  1  0
 1  1   5648 946916 357104 735788    0    0     0   215 14410 14496  2
 2 90  6  0
 0  0   5648 946520 357104 735788    0    0    23   267 13703 14664  2
 2 91  6  0

sar
===
02:40:01 PM     CPU     %user     %nice   %system   %iowait    %steal     %idle
02:50:01 PM     all      2.17      0.00      2.18      4.30      0.00     91.35
03:00:01 PM     all      2.47      0.00      2.23      3.57      0.00     91.73
03:10:01 PM     all      2.29      0.00      2.07      3.77      0.00     91.87
03:20:01 PM     all      2.63      0.00      2.07      3.28      0.00     92.03
Average:        all      2.39      0.00      1.95      4.77      0.00     90.89