>I understand that many (most?) people like to partition their HD so that C: has all the OS and products and D: has all their working (personal) data.
>In such a case they are paying a penalty every time they access their working data because chances are good that the OS or the active programs refer to C: frequently, for anything from their executable components to their temp files in Documents and settings...
>This means crossing the whole of C: including a bunch of empty space every time that happens. And in the reverse direction too.

While that may be true, the total of the time saved by having all of the primary disk in one partition will be lost the day when that partition crashes :).

Didn't happen to me for quite a while, maybe 3-4 years, but still... and I've never lost anything from other partitions.