Well I'm woking on a Vista one and an XP Media edition one. It's not so much the OS but the fact that they come with tons of software both Vaio specific and more general. The XP one has Adobe Premier and lots of other stuff. The client has lost the disks but the drive need replacing. I've tried to recreate restore DVDs using the recovery utility but I suspect that one of the damaged parts of the disk happens to be in the recovery partition - it won't complete making the 2 DVDs.
Ideally I'd love to be able to hand them back like they got them when new but this doesn't look like it's going to be possible at the moment.