Software raid except for ZFS sucks. Uses CPU cycles for processing writes/parity. Software raid is slow and a PITA to deal with.
Linux software RAID performs on par, if not better, than most hardware implementations. Using the host CPU for XOR calculations isn't a problem these days. CPUs are fast enough that unless you've got an extremely CPU bound application on the same server it won't be an issue. Even with SSDs I doubt you'll find a drive or set of drives that can read/write data faster than a CPU can process it.
ZFS is all the rage these days, but I wouldn't subject myself to Solaris just to get it. The features just aren't worth the pain. I'd much rather use a decent system like Linux and live without the extras ZFS brings.