Please have a look at htop screenshot below
You can see there that current host has two CPU cores (or CPUs).
All processes are ordered by CPU usage descending.
So how is it possible that with two processes eating 10% of CPU summary info shows that each of CPU core is loaded more than 50%?
System info: CentOS 5, DigitalOcean
UPDATE
Kernel threads are not hidden in htop settings.
top was showing alike information when ordered by CPU usage (in detail it showed that CPU is significantly loaded by system (~50%) and top processes in its list were using <10% summarized)
This was fixed by server reboot but it is still interesting why that may happen.