I have to say, the NUMBER ONE issue I've had in QBO is with the columns in places like the COA registers.  The issue is two-fold - one being the column widths, the other being the column titles.

The column resizing is not always an easy matter.  As has been mentioned, it can be very difficult to get the cursor exactly right to re-size a column.  And, often, I can't get it to that exact point at all. 

And the default columns that appear are not at all what I want.  I'm constantly using the gear to change which columns appear, but the settings never stay put.  I can leave and come back to find how they'd been originally.

This is extremely frustrating.  I have trouble believing that a piece of software like QBO, with all it's advanced and admittedly impressive functions, is not able to handle something as simple as how the columns work! 

And if anyone suggests clearing the cache, trying a different browser, or even sending Feedback, I've tried all that - it's enough of a repeating theme through the responses here that I pursue those things before anything (and btw, the Feedback button is often totally non-functional).