>>
>> Is anybody seeing a similar problem?
>
> I don't, but I have a switch/hub in between the PCs and Alix.
>
> However I have seen several mentions of similar problems including
>
> http://m0n0.ch/wall/list/showmsg.php?id=344/90
>

What version are you running?  We were plagued with mysterious lockups for 
what seemed to be no reason for a long time.  When were running any of the 
1.2 versions (official or beta) we would see lockups on one of our 
installs - the uptime could be anywhere from 12 hours to 20+ days.  The day 
1.3b1 came out (newer BSD base) I upgraded to that and our issues vanished - 
we have not had a lockup since, and we are still running 1.3b1 (uptime on 
that problem unit of over 340 days right now since last reboot).