I installed Lion last night and spent today figuring out what does - and does not - work. As a huge fan of full-disk encryption (FDE), I'm disappointed in their drive encryption.
RAID may have been improved, but Lion's encryption features, including Time Machine encryption, are not compatible with Apple's RAID.
The diagram at right (from Elementary Information Security) shows how full-disk encryption (FDE) typically integrates into the system software. The diagram doesn't show where the RAID software might reside. I'd expect it to be very closely tied to the device driver. However, it appears instead that Apple placed the FDE below the RAID software. Perhaps this improves performance, or perhaps the choice was driven by design decisions invisible outside Cupertino.
The Time Machine improvement: they have explicitly documented how to switch in a new mirrored drive for an old one. I haven't tried their suggested process since the upgrade. I'd tried the suggested process a couple of years ago, only to have it fail. So we'll see how it goes.