Actually, I'm seeing a 1,000 byte "per day" limit as reported in Daptiv support case #36854.
Here's how we hit the limit: we have a Production Support project for a client with a task named "General Support". There are about 8 support folks assigned to the task. They receive calls throughout the day and log their time to the task accordingly along with any pertinent notes. As soon as the update notes hit 1000 bytes for the day - BOOM!
It's not easy to correct either - as per Daptiv support case #36376. Once they hit the limit for the day they can't enter any more notes.