Change is Good
Steemit made some changes recently which affect us all. These changes were made to improve security and prepare the blockchain for the masses. Many people were using their master key for posting and this is dangerous. People typically don't read warnings and often don't think about security; if I get a hold of your Master Key, your account is now mine! Not everyone understands this principle, they probably think like with most other passwords you just email someone and have it reset. This is not the case. If someone got a hold of your master password, they could quickly change it and you would not be able to do anything about it. Steemit made it much more difficult to use your Master Password on their site by separating Steemit and Steemitwallet.
What to Do?
The safest thing you could do is change your Master Key, write it down, make sure you wrote it correctly and put that piece of paper somewhere safe. Better yet make two copies and store them in separate places, make them waterproof and fireproof. Don't show anyone them and definitely don't write Steem master password and your user name on them in case anyone finds them. There are password storing apps but I don't really trust these, writing down the key is your best option. You will only need it if you forget all your other keys or your phone and computer break or get stolen. Don't store your keys on your computer or mobile device. You can, however, save your Active Key and Posting Key for easy access, these are all you really need.
Many people have no idea where they inputted their keys and which apps have a copy of them. I use Steam Keychain to store my keys by @yabapmatt and @stoodkev I also use Steemconnect. I did not give them my Master Key (they don't store it anyways) although you can use it to import your keys if you don't want to type them in. Using one of these programs makes it a lot easier to interact with the Steem Blockchain (to post, play Drugwars, gamble, use DApps, etc.) Sometimes it is necessary. You can find Steem Keychain at the Chrome Webstore.
Bottom Line, Don't let anyone access your Master Key!
Be careful with your Active Key too, definitely don't give anyone your Owner Key and feel free to share your Posting Key with trusted parties.
I look forward to seeing more changes, let's hope this makes Steem easier for people and leads to fewer issues where people are able to lose their accounts. Remember, if you lose your Master Key you will lose your account.