Google Alert for desktop is a beneficial feature, as it enables the desktop software to notify you when a certain gadget is updated or is attempting to spark your attention regarding a specific event. As there are gadgets for most kinds of Google services that integrate into the main software, you might consider them Google Desktop apps.
The curious thing, however, is that not all of these gadgets have alerts enabled. From the ones I tested, which included many of the usual Google apps, only the Calendar and News gadgets currently support Google Alert. You would hope and even expect that, for example, your desktop Gmail would support alerts but unfortunately, it does not. Nevertheless, some gadgets still do function with notifications, making the Google sidebar a bit more useful. What is even better is that you can configure these Google Alerts desktop apps individually. To achieve this, use the following steps:
On the top of the Google Desktop sidebar, click on the arrow pointing downwards.
Select Configure Gadgets, which is the second option from the top.
To enable or disable alerts you have to select or unselect the box next to that gadget. Notice that these alerts are switched off by default when a new and supported gadget is added, so you will need to enable them as you add them.
Unfortunately, this uniform manner of configuring alerts does not leave any space for gadget-specific notification alterations. In the individual configuration options of the various gadgets, you will not find any configuration options in that regard. Perhaps this would not be a bad idea in order to make the alter system a bit more versatile and customizable.