The limitation on the number of query locators at one time

I am reading the document "AppExchange Web Service Developer's Guide" downloaded from salesforce.com. On the query locator section, it specifies:

"A QueryLocator represents a server-side cursor. A Salesforce account can have up to five (5) query cursors open at a time. If five QueryLocator cursors are opened when a client application attempts open a new one, then the oldest of the five cursors is released."

We have many custom applications and background services using the same account. Those services are running very frequently and retrieving a lot of data through Sforce APIs, so it's very often to use the queryMore function in which case query locator will have to be used, so the 5-query-cursor limitation is very easy to reach. I want to make sure if the 5 query cursors are per login session or per account? if it's per account, we will have a lot of errors in our custom applications.

thanks for anyone who can answer my question.