If you’re going RAID-5, I definitely recommending still doing backups to a separate unit / archival storage. I just had two drives die on my old 0.7TB RAID-5 system, which makes it pretty much a total loss (I’m considering paying for data recovery…).

My new setup will be all RAID 1, with a separate RAID 1 backup unit, and spending some time writing a good backup solution (surprisingly I haven’t been able to find a good program that will do good rsyncing, diffing/incrementals, aging/pruning, and archival/cataloguing).

I’m going w/ eSATA not multilane (as you mentioned, those are rather finicky right now). I’m not worried about SATA II as things are way too much in flux until the real 2.5 spec gets finalized.

As far as drives, I’m looking most closely at the WD WD4000YR for its high MTBF, but will probably mix and match with some Seagate 7200.8′s (I’ll be using SW RAID so I can have different drive brands – that whole trying to avoid simultaneous spontaneous failure thing).