[mynegation]

I used to have 2 monitors side by side turned vertically. The problem for me was that the rotation was down in software in the video driver and many redraws were noticeably slower. It was long ago though (2007 ish), maybe modern performance makes it unnoticeable.

[FooHentai]

The other issue I've noticed is the (polarizing?) filter built into monitors seems to be oriented for landscape viewing only. So when you have screens in portrait, there's no perfect viewing angle that lets you see all the way left to right on the screen surface, without the filter obscuring one of the sides.