I bought my Casascius coins because:

    1. Secure off-line paper-wallet equivalent; cant be accessed over a network and I can put them in multiple locations.
    2. I can give them to less technical friends/family.
    3. Their value may be greater than face value in future.
    4. I'm starting to trust bitcoin more than centralised banking as a place to store my money.
    5. I collect weird currencies.

I've deliberately put half my bitcoins into Mike's coins for the above reasons. I would advise anyone to keep 50% of their coins off-line and if possible split into multiple sub set locations/devices for both on-line and off-line coins.