Such a check would be very useful for checking domains. Right now, a malicious attacker could register google.com, but with one of the characters replaced by a (nearly) identical looking unicode symbol. Then, the attacker could use HTTPS and create a login page identical to gmail's. No, all it takes to get someones credentials are a link to mail.google.com.

It would be nice if the authorities handling the registration of the domain names could forbid domains that look to much like each other.