I dumped my Soft RAID 5 setup last summer. It just wasn't practical.
One of my Samsung P120 250Mb drives failed. It didn't really fail completely but it gave tons of sector errors and I wound up losing a bunch of pictures from a day trip. I RMA'd the disk back to Scan.co.uk and got a replacement. Got the same problem! RMA'd it a second time. They said the drive was fine and gave me my money back. I did a ton of testing of my other disks and SATA connections and still think there's something wrong with either the disks I received or the SATA compatibility.
Anyway, the big problem is that it would take 3 days with the CPU pegged at 100% to rebuild a RAID 5 disk array. Ridiculous. It's possible to live with Soft RAID if nothing goes wrong but it's too painful when it does. It's also very slow writing to a Soft RAID 5 array.
So now I use 2 250Mb drives in a mirrored configuration (RAID 1) for critical stuff. Then I use 2 250Mb drives that are spanned into 500Mb for music and video files. Finally, I bought a 500Mb Western Digital disk that I put in an IcyBox external hard disk enclosure and use to back-up files. This system is working well for me.
I would recommend avoiding Soft RAID 5. Either go with combinations of RAID 0 and RAID 1 or invest in a good hardware RAID 5 controller that offloads the CRC calculations from the CPU.