I have an Esata sheevaplug and don`t have that problem.
So far my plug has been running over 60 days without problem, and the only time I`ve needed to reboot was due to kernel change.
I know from my main P.C that USB drive enclosures can be unstable to say the least at times, have you tested out your drive enclosure on your P.C to see if that is your problem?
Also in my main P.C I fitted a Samsung 1 TB which would work for about 2 to 3 days before my computer would lock up , I replaced the drive for a Seagate 1TB drive and fixed the problem., why don`t ask me.
Yes, before I got my SheevaPlug, I was using this drive with two different machines, one an old laptop that had a USB2.0 PCMCIA card in it. The other was an Atom based PC that had an ESATA port.. Both worked great without this drive ever locking up. I think I'd have no problems with this drive on an ESATA Plug..
This is a 1TB Seagate drie in a "Thermaltake" external enclosure.. I'll be upgrading to a 2TB here soon, because this drive is just about full now.
As for Mark's suggestion of rebooting the plug, I'd rather not.. I've had this thing up to 60 day uptimes a couple times before losing power. I recently picked up an old 500watt UPS and put a huge battery in it. The plug, cable modem, gigabit switch, and USB hard drive are the only things on the UPS, so I expect to be able to keep the plug going for 12+ hours when the power is out, which is long enough to cover all but the very worst outtages we have around here. I already have a "down" script that I run to kill the processes and umount the drive, and an "up" script that does the opposite.. I just want to automate the whole process.. (or fix the stinkin problem! heheh)
I would like to try a different enclosure at some point, see if that really is my problem.. None of the other USB devices crash..