What is account storage?
During the current Beta period, account storage is going to be limited to 100MB (or 100 Notes) per account.
In the future, free accounts will be increased to 1GB storage limit and it will also be possible to upgrade to a Premium account to access even greater storage on one's Doit account.
How do I know how much of my storage has been used?
To check your storage reserves, click the small arrow found next to your name / username in the very top left corner of the sidebar. A drop down menu will appear, showing how much of your storage limit has been used.