What's the best way to effectively report bugs?
The Package you would want to run the Ubuntu-Bug script against is plasma-desktop so th full command would be
ubuntu-bug plasma-desktop
you can run this command from a terminal or by pressing alt+f2 and pasting the command in the text box.
If you find a bug matching yours you can add yourself bay marking that this bug affects you too or starting a new bug if none match your circumstances and give information that it is the Activities plasmoid that is causing the crash/freeze. Obviously you will need to set up an account in launchpad first before reporting the bug.