Disk problems - hard error reading fsbn NNNNNNNN

[Matt Navarre]

After a power outage last night I rebooted my computer and  fsck 
complained of the following :

ad1s2e: hard error reading fsbn 5103776  (ad1s2 bn 5103776; cn 317 tn 
177 sn 20) status=59 error=40

Then goes on for a while giving the same error on blocks 5103776 - 
5103807, except for block 5103777 which has error=01.

Does this mean the disk is failing, or can I just reformat? And what's 
the best way to recover any recoverable data from that slice? 
Unfortunately I don't have a recent backup, since my tape drive joined 
the choir invisible a while ago and I haven't had a chance to replace it.