I would say that depending on what you use your pc for could effect your HD situation.
A lot of guys that do video editing like to use 3 or more drives because they want separate drives for sound source, video source and one for the output file. This way each drive is single tasking.
I would just make sure your os drive is a fast one, doesn't have to be huge, and have a large program/data drive. I would even get a huge external to backup to and keep files that are not accessed everyday. I keep a 500gb external for just that. It only comes on when I need it. I suspect it will last a lot longer that way. Less wear and tear.
I have yet to have a harddrive last much longer than 3 to 5 years before its a gonner,well except for my scsi.