The greatest area of growth was in the wallets containing amounts between 1-5, 5-10, 10-25, and 50-100. The wallets containing 100-500, and 500-1000 grew very slightly, and the wallets containing greater than 1,000 decreased dramatically.
I hate to be "that guy" but this is probably people holding large quantities, splitting up their coins into wallets of 5, 10, 20, 100. Thats the first thing one with a brain does, when one hears that coins are being hacked/stolen.
-B-
The safest place is offline cold storage. The more accounts you have the more complicated it becomes to keep track of the keys. The risk isn't worth it unless you need to hide your wealth...
I know that's likely what MtGox did recently, but the only benefit to doing this is to obfuscate your known addresses and launder the coins through a tumbler service, avoiding legal confiscation at risk of potentially indefinite detention. (refusing to provide keys will put you in contempt until you comply; potentially for life.)
I think trading in the most secure method of storing (the equivalent buying power) of hundreds of thousands/millions of dollars for a complicated/less secure method of storage is unlikely without an alternate motive...
