I have no idea what Vista does, so this may be irrelevant... Anyway, in other operating systems, the ideal state is that the OS uses essentially all memory that is not used by applications as cache. Cache roughly equals to free memory because anything there can be easily discarded and the memory given to applications. But it's better than free memory -- if you need something that happens to be in the cache you don't have to read it from the (slow) disk.
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Re: FUD? (Mike Moyle)
I have no idea what Vista does, so this may be irrelevant... Anyway, in other operating systems, the ideal state is that the OS uses essentially all memory that is not used by applications as cache. Cache roughly equals to free memory because anything there can be easily discarded and the memory given to applications. But it's better than free memory -- if you need something that happens to be in the cache you don't have to read it from the (slow) disk.