To do this right it takes someone who is meticulous.  Who both in procedure and practice builds a system which has a 0% error rate.

Thankfully Casascius is that guy.  I have seen a half dozen threads like this and they all ended up being typos.  It is pretty easy to do since the writing is very small.  A good magnifying glass helps.    It would be nice if clients and websites stated "this is an invalid private key" as opposed to incorrectly stating the "balance/value is zero".  There is a reason for the SHA256 check (ignored by AFAIK every website and client).