Hugo,
 This url may help
http://marc.info/?l=linux-kernel&m=122216518824108&w=2
The kernel version with the problem is 2.6.27-rc....
I'm seeing exactly this problem. The USB Hub times out repeatedly.  
Others are reporting this problem as well. There is a bugzilla number 
somewhere but I can't find it at the moment.
It was not there on earlier 'rc' versions of this kernel.
some of the report seem to point the finger at the USB and how the low 
latency drivers work in a tickless world. There again, I might be wrong. 
What I do know is that I had to reinstall F9 on my test bed Mac Mini as 
F10 after a 'yum update' was totally useless. The USB connected mouse & 
KB did not respond as the USB Hub subsystem kept timing out and filling 
the logs with error messages. This is really noticeable when 'X' is 
running. The KB does respond when in the kernel is in single user mode 
but only works intermittently when at runlevel 3.
Stephen D