One advantage of having a OS-based, software RAID system is in fact that you may change hardware completely and the OS will recognise the stripe/mirror set.

Disadvantage is of course performance.

On a small server here I have a W2K-based Raid-5 system with three disks, and I've gone through mobo replacement (changed brand/model) and OS reinstallation and the software based raid-5 set survived.

Of course the OS was on a different, independent disk, since the OS needs to be up and running to detect a raid set, import it and enable it correctly.