How do hard drives handle bad blocks nowadays?

[rajiv-FrUbXkNCsVf2fBVCVOL8/A at public.gmane.org (Rajiv Aaron Manglani)]

>> Also, should I use 'dd' to test all blocks before I put a drive into 
>> service, or is there a better tool out there?
> Besides the above tests, I've often used dd for reading and writing 
> the entire drive as an extra sanity test, and to force overwrites and 
> possibly reallocate any bad sectors:
> dd if=/dev/zero of=/dev/foo bs=32M
> dd if=/dev/foo of=/dev/null bs=32M

i use dban for new drives hosts i can take offline, or put the drive in another box.