I think it is a nice feature if used sparingly.
Note that while Unicode symbols are a normal part of the Haskell language you can also turn on some Unicode syntax using the UnicodeSyntax [1] language extension. This means the following will be accepted by GHC:
(∈) ∷ ∀ α. Eq α ⇒ α → [α] → Bool
(∈) = elem
You might want to take a look at some packages I created that define some Unicode symbols for common operators and values [2, 3, 4].
Opinions on whether this is a good idea vary. My anecdotal observation is that it seems to be used more by people who speak a native language that is already poorly served by ASCII. Perhaps because they are already used to not being able to simply type every character they need.