Hi Layne. I'm not aware of a way to force users to provide a note when they enter an hour (although I like the idea). Practically speaking, what I personally do is:
navigate to the appropriate item (e.g. Project, Task, etc.)
click the Updates tab (which is normally the first tab, on our layout templates)
click the Log Time tab
(optional...but important) set the Hours Type drop down as appropriate
enter the hour(s) on the day(s) as appropriate
return to the Project level view
choose the Hours tab (from the More button)
choose a special view (once, since it is "sticky") that shows the Description column (and optionally, you could make this "red" if it is blank)
fill in the descriptions on mass, as needed
If people use the Log Hours button instead, the Notes are available at the bottom of the popup, but they're not required, so having a report for the "red" exceptions is likely still a good idea.
Finally, I'd invite folks who like to track their time as they are working to consider our Stopwatch solution, which in many respects is the most mature and timely approach. And if including Notes within Stopwatch (and perhaps even forcing them) would be helpful, please let us know so we can consider it for our road map.
Regards,
Doug