Multiple copies of wallet.dat with a constraint
The risk is if you have shared private keys on multiple computers. Even if you maintain a personal discipline that you won't spend from those other 4 wallets, the risk is still there.  With those private keys still on the other computers, you have opened up 4 additional vectors of attack on your keys, as well as given yourself 5 times the workload securing it all. 

You should only have the private keys for your addresses on the one machine that you say you want to spend from.  

On the other 4, you should only use "watch only" clients, such as the online wallet at blockchain.info or Armory. There are others as well. Both of those wallets will let you set up public keys to watch, but not spend from, because they don't also have the associated private keys. 

Watch only wallets can receive funds just like any other wallet -- you're just watching the balance on the blockchain.