I think the little black swqaure you refer to is just a cue that you are actualyy over an object and if you click it will be selected. Most times this is obvioous and the cue is not necessary, but if you are in Preview mode and turned off the object highlighting it's handy for things you can't see.
I'm not sure if the help files will tell you what all the cursors look like, but there should be a What's New section that you should read. Lots of changes (in my opinion for the better) in selection behaviors.
Very interesting theory, never heard it
It just means your mouse is over selectable object - you can click and select it, than your cursor will change its shape again...
btw, it changes rather often while moving here and there - I think, your best bet is just take time and experiment a bit...
Sounds good to me. Appears to be true.
Thank you. Thank you.
My suggestion to have a way to find "What does this cursor mean?" stands.
If it's in help files, I couldn't find it.
And... I think the answer proves... sometimes it ain't obvious.
Trust me, it's hardly the first time a user has found things less than obvious.