FYI - just got this letter from Coinbase -
Dear Coinbase Customer,
We are contacting you to make you aware of recent developments in a number of proposals for technical changes to Bitcoin. All BTC stored on Coinbase will remain safe during these events described below.
The User Activated Hard Fork (UAHF) is a proposal to increase the Bitcoin block size scheduled to activate on August 1. The UAHF is incompatible with the current Bitcoin ruleset and will create a separate blockchain. Should UAHF activate on August 1, Coinbase will not support the new blockchain or its associated coin.
The User Activated Soft Fork (UASF) is a proposal to adopt Segregated Witness on the Bitcoin blockchain and could result in network instability. It is scheduled to activate at the same time as the UAHF.
To ensure the safety of customers’ funds, we will temporarily suspend BTC deposits, withdrawals, and buy/sell starting approximately 4 hours before activation of either fork.
If you do not wish to have access to UAHF coins, and do not wish to access your BTC during the fork, you are not required to take any action.
If you do wish to have access to UAHF coins or access your BTC during the fork, you should send your BTC from Coinbase to your external address by July 31.
For more information on these potential Bitcoin forks, please refer to this article: https://support.coinbase.com/customer/portal/articles/2844217-uahf-uasf-faq.