I'm actually a fan of using Unicode in my code. As people like to say, code is read more often than it's written, so I'm willing to make typing a bit harder in return for making the code prettier.
Happily, typing Unicode characters is quite easy with a good editor (Emacs). I use the TeX input mode which just lets me use TeX names for symbols, but somebody has actually written a Haskell-specific mode which might be even better[1]. I might try it some day.
One peculiar habit I have is using x₁ x₂ x₃ instead of x1, x2, x3 or x_1, x_2, x_3. I definitely find the Unicode version easier to read and work with, although it probably helps that Emacs highlights the number in a different color.
Unfortunately, this is a minority opinion at the moment. Even in *this* day and age, people still find Unicode too difficult to type!
For my internal code, this is not a problem, but it's kept me from putting any Unicode in public APIs. Shame.