The curved drop shadow phenomena is a design trend that needs to stop.
They make me want to throw up by creating an impossible surface
The intent is to make the image corners appear curled. It fails horribly. For the effect to work, the corners would need to be visually warped. They aren't. They're perfect 90 degree angles. This makes it appear as if the image is sitting on a curved surface.
If you have any degree of spatial aptitude, the above image should make you nauseous. The text is sitting on a curved surface yet is not warped. It is an impossible structure. It's like reading text on a patterned background. It subconsciously damages reading comprehension, causes indigestion, and degrades your credibility as a designer.
It's copycat design that serves no purpose
This shadow trend is the glossy reflected logo of our web era. It's the zigzag divider edge. It's the blink tag. You want to make your site look like a wavy impossible surface? No, you don't. You want to keep your integrity by not copying a design trend that has no substance. Your design should complement content and serve specific and important purposes.
Friends don't let friends copy design trends. Be accountable for what you add to a website visually. If you find someone using them, yell at them. Real loud.