Constraints or flexibility?

Google Calendar and Yahoo! Calendar use very different mechanisms for the "quick entry" of events.

Yahoo uses separate fields for each component of the event:

Google on the other hand uses a single text field:

Both approaches have advantages and disadvantages.

The Yahoo approach--using separate, specified fields--is probably more suitable to novice users because it ensures entries are in exactly the right format. But, it is likely slower than entering information as a single text string.

The Google approach reflects how people might quickly jot down events in an off-line context. But this also requires more system logic to properly interpret user's entries--and this approach runs the risk that users may not use  syntax that the system can interpret, resulting in errors.

For example, consider this quick entry in Google Calendar:

breakfast w/Tracy at 7

With this entry, Google incorrectly schedules the breakfast with Tracy 7:00 pm rather than 7:00 in the morning (which was the user's intention).