When OS is booted and UltraVNC is started in service mode, controlling of PC leads to very high CPU usage (>10x higher than in application mode).
Uninstalling the service and installing it again can fix the problem, but only until next reboot.
Version: 126.96.36.199 (ultravnc_32_1212.zip)
OS: Windows XP SP3
Here is the screenshot of task manager: