I wrote that I blamed the rather odd behaviour my laptop was showing on some kind of hardware fault - possibly the lid switch. However a quick swap of hard-disks with Steve proved that whatever was wrong was on my hard-disk and not on his. So it was software ... I heard from someone in Microsoft that one of the Vista updates seemed to have broken sleep for him as well. We call these things where one fix breaks something else "regressions", but this one seemed odd. Someone else told me about two patches both described as "An update is available that improves the compatibility and reliability of Windows Vista" which had fixed a lot of minor issues for him. The links and descriptions are as follows:
Not hugely informative descriptions and the text at the download pages didn't mention sleep. But having installed them the sleep problems have gone, a couple of things seem to have speeded up too. It could be these, it could be the last lot of fixes which windows update marked as important, or it could be something else.