Some months ago I started a thread on this forum entitled 'Backup - should it be as hard as I find it?'. The slowness was particularly noticeable in Backup. No solution was found, and I gave up. Obviously I've been using other backup means since then.
So, I decide to have another go at this, and since I no longer seem to be able to add to that thread, the solution I found is here.
I looked at Support -> Technical Support -> Top Tech Issues-> 'My Computer runs slowly after install of Norton 360' and found that I needed to uninstall my old Norton product before installing the new one. The problem was fixed by following the instructions - downloading an uninstalling tool and reinstalling Norton 360.
My PC now boots at an acceptable speed, and Norton Backup works at an acceptable rate.
However, if I try to use Norton Backup, it fails to backup almost 2/3rds of my files (My My Documents is about 30gB, if I tick all the boxes in the 'What' section of backup, Norton only reports that it's going to backup 10gB, and if I go to the details of each category, I can see items not found, so as you can imagine, I won't be using Norton 360 to back up anything soon).
In fact after this experience, when my subscription runs out in 550 days, I'll be looking elsewhere for a security product.