Can anyone explain these bandwidth download spikes that are linked to bitcoind? I am running bitcoind on a linode.com vps server and they provide some really great graphs to the owner of the account.

I logged in and noticed these spikes the other day: http://i.imgur.com/aWoWfie.png

Every minute that those graphs were being generated, bitcoind was running at about 400MB of memory usage and exactly 10 connections to the Bitcoin network.

Any anyone explain the green download spikes shown in the picture I linked to above?

I am positive that I did not upgrade my system or perform and other downloading during the time frame seen on the graphs.
The green in your graph indicates outgoing traffic. More than likely, those spikes indicate transfer of blockchain or unconfirmed transactions to newly-initialized nodes in the Bitcoin network.