Coinbase can "limit" your account for using altcoins.

[BayAreaCoins]

https://support.coinbase.com/customer/portal/articles/1905681-localbitcoins-and-coinbase

Coinbase neither prohibits nor endorses our customers’ lawful use of any third-party exchange service. Nor do we necessarily prohibit our customers’ sale of bitcoin in peer-to-peer transactions for personal, non-business use.

Coinbase customers may not, however, use their Coinbase Accounts to engage as a business in the exchange of virtual currency for fiat currency, funds, or other virtual currency. Coinbase reserves the right to limit your account use if we detect activity which constitutes a violation of this policy and/or our User Terms. We further reserve the right to limit your account use if your account is associated with high-volume activity inconsistent with personal use.

Be safe out there folks.  

[NorrisK]

Basically they say that if you use it for normal personal use there is nothing to worry about.

Just don't use bots or clearly use the account for business transactions.

[UFCkid]

Still a joke. 

[KhalDrago]

I like coinbase

[unusualfacts30]

https://support.coinbase.com/customer/portal/articles/1905681-localbitcoins-and-coinbase

Coinbase neither prohibits nor endorses our customers’ lawful use of any third-party exchange service. Nor do we necessarily prohibit our customers’ sale of bitcoin in peer-to-peer transactions for personal, non-business use.

Coinbase customers may not, however, use their Coinbase Accounts to engage as a business in the exchange of virtual currency for fiat currency, funds, or other virtual currency. Coinbase reserves the right to limit your account use if we detect activity which constitutes a violation of this policy and/or our User Terms. We further reserve the right to limit your account use if your account is associated with high-volume activity inconsistent with personal use.

Be safe out there folks.  

Cliffs:

Coinbase is a merchant who sells bitcoin for $. Don't use them as an exchange. Use BTC-E instead if you want to day trade btc to $

[meadefreling]

There are other options for US residence but coinbase will only loose more customers.