We all love receiving scraps, but constantly checking back to your scrapbook page can be tedious. How many of us have our scrapbook page open and are clicking refresh on it constantly!
With scrap alerts you can be on any orkut page and find out that you have received a scrap - that very minute. You could be browsing your friend's photos, and find out "hey! I just got a new scrap." Then you can click on the "Scrapbook" link to reply on the spot. This way you'll be free to explore all of orkut, comforted in the knowledge that when you have received a new scrap, you'll know about it that moment.
We'll be rolling this feature out over the new few days for all users, but If you really prefer clicking the refresh button all day long, you can go to settings to disable to the feature.