I use amanda, and use 'amverify'.  It doesn't compare  the bits, but
it does read the files back and run them through gunzip and restore
tfv (or tar for those that use tar, which I do for coda but not ffs).
I am betting that if gzip doesn't get a decompression error that the
bits are ok.

In an ideal world we'd do a test restore once a month, where we pick a
random person, ask them to pick an arbitrary 'important file', and get
it back.  In practice, the above level of verification has been
sufficient to ensure that the twice/year we really need the bits back
we've been able to read them - the flaky part has been tapes (DDS) and
(once) the scsi bus (I think), where data read back without errors but
was trashed (gzip failed).

-- 
        Greg Troxel <gdt@ir.bbn.com>