I wrote about having switched to libata - but now I’m back to the old IDE driver. You can read about the reason in this mail I sent to the linux-ide-mailinglist.
Update (2007-07-17): Had two freezes again, _without_ libata. So I sent this mail to the linux-ide-mailinglist. I guess I’ll run a memtest session tonight…
It was actually a strange hardware problem (or so I think). I bought a new laptop.