I think we're getting a bit carried away here... the original question was:
"is there sensitive personal info I need to be aware of that needs to be backed-up and removed"
First thing to establish is what do you use the machine for? I interpret your question to suggest that it is just a general use machine and you're concerned because you have personal info on it, maybe access your bank online and are worried about passwords etc being recovered from the drive - as opposed to having commercially or nationally sensitive information which would be security classed.
If this is the case then there is a slim chance of any harm coming to you even if you don't do anything to the drive. If you would like be safe just in case (always sensible) then backing up your files, pictures etc etc on a usb stick and performing a few formats will be more than is required for general stuff.
If you would like to be a bit safer still then a third party bit of software which wipes and over-writes the drive can be a good way to go.
As for physical destruction, that would certainly invalidate your warranty making the whole issue pointless as you may as well just go out and buy a new drive and not bother with Dell at all.
I work in a VERY security sensitive job and the UK government guidlines state that commercially sensitive drives need to be wiped and data blitzed and any drives containing RESTRICTED or higher (confidential, top secret etc) must be physically destroyed in a controlled manner - i.e. put into a shredder where the chips that come out cannot be more than 2mm pieces... this is massive overkill for someone worried about protecting their personal data.
Dell have a corporate responsibility to treat your data properly. If you send your drive off and they replace it chances are your drive will be destroyed. There is a possiblility that the drive is repaired and sold on as a refurb but even in this case they will have to use an accredited process for wiping the drive clean to international ISO standards.
Put simply, for general use I would back up my stuff to a USB stick, and format the drives a few times... maybe go for a utility to effectively brick the drive such as one suggested by jonuk76.
Edited by lsmeed, 06 January 2014 - 05:12 AM.