Nova is one of the few exchanges that has handled their problems well. When they made the decision to close down, they notified the community well ahead of time so everyone could get their coins withdrawn. After making that announcement, there was a bid to buy the exchange. They were also fairly transparent about that fact and kept the community informed enough to make good decisions.  A very good example of an exchange that went defunct the right way was safecex. They had to shut their doors, but notified everyone in plenty of time.

I learned the hard way not to keep large amounts of coins in any exchange. When I send coins to an exchange, I no longer have control of the coins because the exchange now has the private key to the address that I sent the coins to. When I send coins to an exchange what's actually happening is a trust agreement, I am saying "Here, I trust you to hold my coins so that I can use them for trading"

Exchanges all have a target printed on their back. They also ALL have disgruntled users who hate and post about anything they don't like.

Take a quick look at some of the posts around here

EDIT: and here