Do I need to wait 3 days for trades to settle like normal stocks? Or can I just jump in and out of USD/BTC constantly?
Settlement occurs at the time of order execution..
Also is there an easy way to keep track of trades for taxes? Anything else I should know before trading?
Market orders are dangerous due to "Gox Lag" (delays between when the order is entered and when the order matching engine actually processes the order.)
Withrawals (either BTC or USD) may not be processed immediately.
When you leave funds at an exchange you are trusting that the exchange is competent enough store your funds securely, and that they are trustworthy. Additionally, username and password is an insufficient protection for an account holding non-reversible funds. Instead you want to make use of the two-factor authentication (2FA) using Yubikey, Google Authenticator, etc, to protect your funds from being stolen via a replay attack (should your computer become compromised).
