There is a difference between what looks good in a print viewed by ambient light and what looks good when projected onto a screen or viewed on a monitor. A further consideration is the ambient light when viewing on a screen.
White or a light colour is the biggest offender as the large expanse of it dazzles the eye and affects one's appreciation of the image itself. This doesn't happen normally with a print viewed by ambient light but projected the white is the brightest thing the eye can see and unless strictly controlled is bad.
My rule of thumb for an image of about 800 pixels wide is a white border of 4 or 5 pixels, when I first started organising for projected images I was warned that a one pixel border could get 'lost' by the projector. Since I use the 'dark' option here at CiC I tend to forget that others may not and images need a border as say at PhotoNet or elsewhere with white screens.
White is a prefered colour for mounted prints, though my preference and use is a mid grey mount with perhaps a white border occasionally, and this and the rules for using it seem to unfortunately been transfered to digital
As for drop shadows .... YUK

as well as some of the 'pretty' presentations that are inflicted on the viewer.