Considering the fact that transactions are somewhat anonymous, having mutliple address is the best way to manage where the coins are coming from. Just be careful to make a new backup if you go over the basic 100 addresses.
Make backups on a regular basis even if you don't go over 100 addresses.
Assuming you are using Bitcoin-Qt for your wallet, it creates a new address (that it keeps hidden and doesn't tell you about) every time you create a new transaction. It moves some of your bitcoins to that hidden address. So if you create only 25 addresses, but you also send 80 transactions, then you have used up more than the 100 future addresses that were included in your last backup.
