I've had a 3ware RAID card for a couple of years now, with 4x500Gb SATA disks attached. Driver support under both Linux and Windows (2003 x64) is excellent.

These days, I'd probably opt for software RAID, whether Windows or Linux, mainly because if the card fails, you've got to find a compatible one to access your data, whereas with software, you just boot up another PC with the same OS (I do back up my data to an external disk every month or so, however). Software vs. hardware performance is irrelevant these days for most purposes.