The windows team have said this:
Will Superfetch be disabled on SSDs?
Yes, for most systems with SSDs.
If the system disk is an SSD, and the
SSD performs adequately on random
reads and doesn’t have glaring
performance issues with random writes
or flushes, then Superfetch, boot
prefetching, application launch
prefetching, ReadyBoost and ReadDrive
will all be disabled.
Initially, we had configured all of
these features to be off on all SSDs,
but we encountered sizable performance
regressions on some systems. In root
causing those regressions, we found
that some first generation SSDs had
severe enough random write and flush
problems that ultimately lead to disk
reads being blocked for long periods
of time. With Superfetch and other
prefetching re-enabled, performance on
key scenarios was markedly improved.
Source: Engineering Windows 7
So it seems that disabling Superfetch isn't a guaranteed way to check things. I'd guess that it's working fine, as long as the correct drivers are being used.