I dont know, if anything was changed in A5 in this regard but I do find it very tricky to find the point, where the mouse-pointer turns into the trim-tool at the beginning/end of regions.
Is there some shortcut that switches the pointer to the trimmode so I do not have to find the seemingly small margin where the pointer reacts in the GUI?
Yes a bug report has been filed already. I found a workaround of sorts. First zoom in so far that you can see the fade ins / outs Ardour automatically adds to regions. Then zoom back out, now the area in the beginning / end of a clip where the mouse turns into the trim - tool is much wider.
I found that workaround also, it can help but is not much preferable, when you want to trim 20 seconds at the beginnung of a recording because you need to zoom far into the fractions of a second level. I also noticed, that the switch is slightely better to find, when you drag the mousepointer from hovering over the region towards the end you want to trim.
But as the good guys are on it, I am sure, that we have that funcion back as good as it always was before long
Bug is now fixed in git. The nightlies that will build (for Linux + Windows) tonight (August 18th 2106) will have the fix; it missed the cut-off for OS X for tonight, but will show there tomorrow.