Had an unpleasant thought walking the dog this morning!
I have a 2 1/2year old Vista 64 machine with Intel Q6600, overclocked to 3.00Ghz, 8GB RAM and 2 x 640GB HDDs in a RAID 0 array. (You can see this as an attempt by someone with a dangerously small knowledge of computers to achieve maximum speed with minimum cost - I wouldn't go down that route today).
I back up with Acronis True Image. (Also copy all image files to DVD). However, it occurred to me that in the (not unlikely) event of a HDD failure, I might choose to replace the whole set-up rather than replicate the RAID array with new hard drives. In which case the back-up is useless as it would only restore to the existing machine, with replacement hard drives, in the same configuration. This is correct, yes?
As a supplementary thought, I bought a fairly high spec Thinkpad W520 (i7, Win 7 64, 8GB, better graphics card than desktop) recently on the basis I would be doing a lot of PS/Lightroom work away from home - false assumption as it turned out and an unnecesssary duplication. Given I don't have massively large files to work with (5D2), if RAID machine falls over, I thought rather than replace it I would just use this laptop with the external monitor and get a big external hard drive for storage. I suspect this would be at least as fast because of the more up to date processor and OS.