I have a 10" fresnel that's been converted to strobe (Norman used to make these), and except for motion artifacts and pupil effects like those mentioned above, you can't tell it isn't a continuous light source.

There are some kinds of light modifiers though that are just more practical with strobes, so you can usually identify, say, a softbox, and you can usually assume that there's a strobe inside it, though there are fluorescent arrays that look like softboxes.