Categories in the gnome-shell dashboard are removed in GNOME 3.8. All application icons are there and you need to know the name of the application to search for the icon in the shell dashboard. This is a half-cooked feature change. The ultimate aim is to provide a custom grouping facility for the user to group applications together, instead of gnome-developers or the application-developers decide which exactly is the category of the application. But the customisation options are missing in GNOME 3.8 and is expected only in GNOME 3.10, which is expected to be released in September 2013. I read about enabling these categories in here. There might be more information available on some other website, but the way I used to bring some categories back is below.
1. You need to add a few entries using the dconf editor from the shell.
3. On the right side edit the app-folder-categories. The default is ['Utilities', 'Sundry']. Edit this line by double clicking it and replace it with this ['Utilities', 'Games', 'Sundry', 'Office', 'Network', 'Internet', 'Graphics', 'Multimedia', 'System', 'Development', 'Accessories', 'System Settings', 'wine-wine', 'Crossover', 'Crossover Games', 'Science', 'Education', 'Universal Access', 'Other']. Earlier I had posted a smaller list, thanks to all who commented on this post, now you have everything to move the icons to categorise almost all programs. New screenshots of my gnome-shell with some app-categories are below. All programs now in a category or another.
Update (2013-05-27): More categories added. There is no stray (ungrouped) app icons now. The above change is managed by adding a new category called Others. In 3.8, even though we add a category and the program access icon is added to that list, another copy is still active in the old place. All these are moved to the Others, just to make to look it neat.
Update (2013-11-23): One reader (Pillenski) has commented that by using “wine-wine” in the list can enable grouping of wine icons. I have not tried this as I stopped using wine and started using virtual machines.
Update (2013-11-29): More categories (wine-wine (thanks to Pillenski), Crossover, Crossover Games (thanks to Enio), Science (thanks to Regs)) added based on user comments.
Update (2013-11-29): Two more categories (Universal Access and Education (thanks to Daniel)) added based on user comments.