Up until recently, it has been considered sacrosanct that deposit holders be protected, no matter the cost. The convention and social contract has been that you deposit money for safe-keeping in a bank. We have seen this over the past few years across both Europe and the US, as insolvent banks have been bailed-out, nationalised, given secret loans, so that deposit holders are wholly protected.
With Cyprus, this widely held belief is now in tatters. You as a deposit holder are now a creditor of the bank. As soon as you lend your money to the bank, it is no longer yours. The bank will provide you with interest for the duration of the loan. If the bank is no longer a going concern, you will no longer receive special treatment, but instead you must get in line with other creditors.
Some may argue that this has always been the case[1], however it will be a genuine shock to many people, and any faith in deposit guarantee schemes has been dealt a severe blow when a week ago, the EU urged Cyprus to collectively punish all deposit holders regardless of balance.
[1] For those in the UK, the House of Lords said in Foley v Hill 1848 http://www.uniset.ca/other/css/9ER1002.html
"Money, when paid into a bank, ceases altogether to be the money of the principal... The money placed in custody of a banker is, to all intents and purposes, the money of the banker, to do with it as he pleases... he is, of course, answerable for the amount, because he has contracted, having received that money, to repay to the principal, when demanded, a sum equivalent to that paid into his hands... the banker is not an agent or factor, but he is a debtor."