Hard drive: Is bigger better?

I have a new PC with 60 GB hard drive (my old PC had 15 GB). I was going to
get an enclosure and another hard drive anyway to do backups to via USB (I
don't have an extra bay for a removable docking drive). However, with the good
prices (after currentt rebates) on 120 GB drives, I'm tempted to get one of
those to use as the main drive since it comes with an 8 MB buffer that my
current drive doesn't have. Both drives are way bigger than I need at this
point, but allows for growth. So I can move the current 60 GB drive to either
the second internal drive bay to use for the windows pagefile and for ghost
images and data backup, or I can put it into an enclosure and do the USB thing.
Any recommendations, pluses or minuses? I've also seen some 80 GB drives at
the same price as 120 GB recently; are there any reliability issues related to
size? Thanks.

GS