I was having very slow startup after the GUI was established. The UM System monitor told me it was doing something 'big' with the CPU but it was not showing much disc activity. The processes seemed to be mainly 'await' with very little else, ie the cores were not busy. It took me about a month to figure this out, as a result I am not feeling as confident as I was. ie overwhelmed by feelings of Newby-ness.
All it took to cure the problem was to empty the Rubbish Bin. For some reason UM is obsessed with peering into the Rubbish Bin for about 3-4minutes if you have it chocker block like I did. I had recently installed a clean UM system and liking it very much, but I carried over a couple of legacy folders from previous disks, then sorted through them and deleted old stuff, duplicates etc
Probably a widely known fact, but as the Coasters sang "Take out that paper and the Trash, or you don't get no spendin' cash"