Post production sharpening is a touchy subject.
Too much sharpening, and your footage will undoubtedly look like shit. Too little, and you might as well have spent your time doing something else. Casey Faris, whose various post production tutorials have been featured on this site many times, recently put together another one that shows you how you can achieve fantastically sharp and detailed images without many of the pitfalls associated with sharpening in post.
To boil this tutorial down to its essence, it's usually best avoid the basic "Sharpen" filters in whatever post production software you happen to be using. Instead, Casey recommends the "Unsharp Mask" effect that comes standard in all Adobe video apps. Contrary to its odd name, the unsharp mask is basically a sharpening filter that adds in a few extra parameters that you can control individually. For actually sharpening footage, he uses a technique in which he pushes each of the three controls past the point where the footage starts to look unnatural, and then dials each one back to the appropriate level of sharpness. This technique makes it easy to achieve the maximum level of sharpness without the image starting to look unnatural.
Also, while there are absolutely circumstances in which post production sharpening is necessary, I'd be remiss if I didn't say something to the effect of, "sharper images aren't always better." With camera resolutions pushing higher and higher every year, lack of image sharpness and detail aren't really something that most of us will ever need to worry about going forward. Add to that the fact that super sharp images can be unflattering to talent, particularly in closeups, and it's clear that there definitely needs to be some balance and nuance in terms of why you choose to sharpen your images.
How do you sharpen your footage in post? And more importantly, under what specific circumstances do you sharpen? Let us know down in the comments!