as someone mentioned...the size difference could also be key. i'd say it's more than a slight difference. i use mine to work out a lot. if you plan to do this, or use it in nondescript ways, go with the mini.
i also endorsed the mini because everyone i know who got the mini loves it, and most everyone i know who got the big one wishes they got the mini.
the average mini holds roughly 1250 songs. let's say a cd holds 12 songs...that's more than 104 cd's worth of songs. compare that with the normal ipod, which will hold in the ballpark of 6,500 songs--that's more than 520 cds. if you have 520 cds you're dying to download onto your computer and transfer to your ipod, or you are rich and want to buy an anus load of songs at 99 cents a pop, go for it. but the mini is really plenty of space for most people.