I haven't been able to find this report or something similar here, but if this is already something know, sorry for the duplicated report.
In a system with many processors, the information panel is too wide.
My screen is set to 1920px and only 6 cpu's fit on it.
Linux patito.local 2.6.36-gentoo-r5 #9 SMP Mon Jan 24 10:47:15 MYT 2011 x86_64 Intel(R) Core(TM) i7 CPU Q 820 @ 1.73GHz GenuineIntel GNU/Linux.
Fixed in http://git.xfce.org/panel-plugins/xfce4-cpufreq-plugin/commit/?id=5327de3b636b306439c5ab9943a94f718dba108f.