[CentOS] Alarming (?) smartd reports

I decided, after the last discussion of smartd and S.M.A.R.T. disks,
to take a look in my /var/log/messages, and I'm seeing fair bit of
this:

Sep 10 20:11:23 mhrichter smartd[3361]: Device: /dev/sda, 4294967295
Offline uncorrectable sectors
Sep 10 20:41:23 mhrichter smartd[3361]: Device: /dev/hdb, 21 Currently
unreadable (pending) sectors
Sep 10 20:41:24 mhrichter smartd[3361]: Device: /dev/sda, 4294967295
Currently unreadable (pending) sectors
Sep 10 20:41:24 mhrichter smartd[3361]: Device: /dev/sda, 4294967295
Offline uncorrectable sectors
Sep 10 21:11:23 mhrichter smartd[3361]: Device: /dev/hdb, 21 Currently
unreadable (pending) sectors
Sep 10 21:11:23 mhrichter smartd[3361]: Device: /dev/sda, 4294967295
Currently unreadable (pending) sectors
Sep 10 21:11:23 mhrichter smartd[3361]: Device: /dev/sda, 4294967295
Offline uncorrectable sectors

Clearly there is a minor problem on /dev/hdb, which doesn't really
surprise me, nor is it particularly worrisome (because I don't use
that drive much).

However, the other one I find more than a little curious.

/dev/sda is a Seagate 300GB SATA drive that's coming up on two years
old next month, but the number of "Currently unreadable (pending)
sectors" or "Offline uncorrectable sectors," depending on which one
you believe, is interesting - 4294967295 is FFFFFFFF in hex, and I'm
running a 64-bit machine.

Google is not particularly informative on this subject - anyone know
more than general suggestions about dd, badblocks, etc.?  This is my
boot and primary system disk (has been for some time), but the error
message is essentially meaningless (to me, right now).

Thanks.

mhr

PS: In the last couple of months there was a discussion of how to make
the disk less active, starting with someone reporting that their disk
drive activity light blinked every 30 seconds or something like that.
I tried to find it again, but I couldn't pin down what to search for -
what was the solution?