Reboot into Safe Mode too, delete it and I assume along with the app are other elements you may have to search for, such as any plug-in it installed or use?
If so, they should have created an uninstall/installer.
Uninstalling Dropbox will not delete your Dropbox account or remove the files in your Dropbox folder from your hard drive.
https://www.dropbox.com/help/41
- Quit Dropbox (click on the Dropbox icon from the menu bar, click on the gear icon, and then select "Quit Dropbox").
- Drag-and-drop Dropbox to the trash from your Applications folder.
- Your Dropbox folder and its contents will remain intact. However, if you'd like to remove that as well, you can drag and drop your Dropbox folder to the trash.
Uninstalling the Dropbox contextual menu:
- Open the Finder and select Go to folder... from the Go menu (or press Shift-Command-G).
- A dialog box should appear. Now copy and paste the following line into the box and press the return key:
/Library
- Delete the DropboxHelperTools folder by moving it to the Trash.
(Optional) Removing your Dropbox application settings:
- Open the Finder and select Go to folder... from the Go menu (or press Shift-Command-G).
- A dialog box should appear. Now copy and paste the following line into the box and press the return key:
~/.dropbox
- Remove your Dropbox application system settings by selecting all files in the folder and dragging and dropping them into the trash.
http://www.bing.com/search?q=uninstall+dropbox+mac