I realize it's all startup-y to pat yourself on the back about growth, but aren't you painting a target on your back for those that want to perform the next heist?
On average 98% of customer bitcoins are held in cold storage...Offline wallets are generated from an offline system and kept in paper format in three separate locations, using a technology based on raid.
https://bitcointalk.org/index.php?topic=23938.40
http://www.managementtoday.co.uk/bulletin/mtdailybulletin/ar...
But of course, they weren't really in cold storage or offline after all, because somehow they all disappeared...
Not that I mistrust coinbase specifically, but without insurance, audits and regulation (i.e. without a banking license), I'm not sure I'd trust anyone to store significant amounts of money.
Unproven claims aren't worth much.
Under the assumption that the crypto used in Bitcoin is safe, there's, for example, nothing an attacker can do to spend the coins in offline wallets. Not even a 50%+1 attack that'd be sustained for days...
If anything, the recent fiasco with Gox (which is more than shaddy) gives me lots and lots of confidence in Coinbase to do "the right thing".
Now I'm not saying they'll never get pirated or anything like that. But Bitcoin implemented correctly seems to be very safe and there are many people out there who have bitcoins which are "sleeping" safely on offline wallets in deep cold storage.
Most people holding bitcoins and most companies like Coinbase only need a fraction of their bitcoins "online" to be able to operate. And even for those bitcoins I take it Coinbase is taking security very seriously.
The biggest thing that gives me pause about Coinbase is their decision to use MongoDB. There may be a reason, but I certainly can't find one. Their use case is perfect for proper, old-fashioned, reliable RDBMS. They've also had a fair amount of customer service issues, including "we rebooted and our job queues didn't run anymore" problem where they tried to rip that guy off.
Even so, the security of the offline wallet is so important, you'd think their investors will have insisted on some auditing and third party implementation. Maybe some of the big wallets are even partially held by outside people.