Q:

How much internet bandwidth does keeping a Ethereum wallet use? 

I have limited internet (250 GB per month) which I share with multiple people, so I have to make sure I don't use up too much.  I downloaded the Ethereum wallet client, and it seems to take quite a while to sync.  Will Ethereum use a considerable amount of my internet bandwidth? 

A:

The Ethereum Wallet runs the geth client which is a full Ethereum node. 
You can see my monthly bandwidth in How fast should be an internet connection to mine ETH?  for a single geth node with 2 x ethminer mining instances, so my statistics should be similar to running the Ethereum Wallet continuously:

My monthly estimate from the charts above would be between 32 to 54 GiB downloads and between 25 and 91 GiB uploads, with the total transfers between 73 and 141 GiB.

If you only run the Ethereum Wallet periodically, geth will catch up with the mined blocks in the blockchain and you will skip receiving and transmitting all the transaction data that geth processes when it is online.