Yeah, I've seen a lot of thumbnails where all you can see is a lewd expression, or a nipple

I thought that was something done by the site more or less automatically (the close crop anyway) — I wouldn't otherwise expect everyone to crop the hell out of their works.

In any case, it's the most annoying feature of this site, for me.

Yes.... that IS a SINGLE one of my spots I zoomed in on for the tumbnail..... Wait.... people can't get context of a picture from a single cheetah spot? O-o

I have to agree, and I think the site autocrops them.

Yeah, the site tends to try and make square thumbnails by just taking a centered square and cropping off the longer dimension. So tall images tend to show nipple to knee.

I intentionally crop to facial expressions/bust shots. Its simply my prefference.

plus if you dont select a thumbnail deliberately the site does also auto crop to a certain degree for thumbnails, esp for large images, so those weird zooms are often a result of the autothumbing.

I'm personally more attracted to a drawing's style than subject, so I'm quite fine with sensible close-ups.
I think the best is when it's possible to recognize the style or the artist from the thumbnail while also hinting at what else is in the picture, e.g. nudity or somesuch.

The cropped thumbnails are the worst part of Weasyl.

This cropped thumbnail is the best cropped thumbnail everrrrrr…!

Weasyl will Autocrop your images if you do not select a suitable cropped image that you've made yourself or one when you are uploading to Weasyl itself.

I don't really mind the thumbnail thing that much, but that is good advice.