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.
It would clearly help for the system we have now but the real solution is to push for stricter authentication across the board. As convenient as URL strings can be, we need E-mail clients and other tools to be able to force at least a 2nd layer of authentication (e.g. E-mail claims link is from ___domain #1; user must counter by selecting from a list of sites actually visited previously, and E-mail client refuses to open link if they don’t match). You could imagine much more elaborate solutions too based on certificates, etc.
I don't think that particular solution would be good from a user experience point of view, but it is indeed a nice idea to filter out domains that you have received emails from (and are not deleted or in the spam folder).
However, there are ways around this too. I think the fundamental mistake was to allow (all?) unicode strings as urls. However, I can't come up with an elegant solution on the spot (since it would be unfair and unpractical to use ASCII for this).
It would be nice if the authorities handling the registration of the ___domain names could forbid domains that look to much like each other.